So I suppose my question is, with a fantastic reading of 6.7 after 4 hrs how could I know what would happen over the next 2 hrs?
Short answer is - you couldn't! I would have done the same as you. In fact I had a very similar situation happen to me recently, I forget now what I had had for dinner but it was something pretty carby and I had already injected something like 14u for it in a split dose. Tested before bed and was 8.something, thought "yay I got it right for once!" In the back of my mind, I knew that there was a chance I might be wrong and still need yet more insulin, but knowing I still had IOB left, was hours out from the meal and was about to go to bed, the possibility I might just have "gotten it right" for once was equally strong - and if that was the case, and I added more insulin, I'd risk a nighttime hypo. So I went with my gut, assumed I was spot on, and went to bed without correcting. Woke up at 16 something. Dammit.
You just can't predict how every situation will go and get it down perfectly. Oddly enough, I find that life with insulin is actually LESS about mathematical precision in my BGs than it appears to be for D&E T2s. If I stopped to analyze every time my BG didn't do what I thought it would by 1 or 2 points, or heck, even by 3-5 points, I would go insane. There's just too many converging factors that I'd never be able to pin down with any certainty. That's why you can do the same thing on different days and get different results.
Of course when you're learning, as you are QL, what is the most likely "best response" for various different situations, it DOES pay to analyze these things a bit. But it's normal for it to be crazy-making, so learning to let go ("huh. That happened. I don't completely know why - and I guess I never will now! Oh well, what's done is done!") and move on is another important skill to acquire! One as vital to my own continued survival and sanity, anyway, as carb counting.
As to actual, concrete advice. Something I ran across quite a while ago, forget where now (could probably find it again if I looked though), but the idea was that above a certain amount, 30-40g for most people, the insulin-carb relationship "goes non-linear." That is, if your ratio is 1:5 and you eat 30g, you'll likely need 6u to cover that meal. On the other hand, if you eat 60g, you'll likely need something like 15u or even 18u to cover that meal - not 12u as the math would predict. I have certainly found that to be true in my case!
Timing also goes non-linear at that point. That is, where with a smaller and/or lower-carb and/or lower-fat meal, I can probably count on a "normal" post-meal curve, rising for the first two hours and falling again for the rest, and hopefully back where I started by hour 4 or 5, for a larger/higher-carb/higher-fat meal I don't always know what to expect, but I know not to expect it to behave normally! Usually I will see like you did, the meal will take longer to digest than the insulin duration, so that once I hit the 5-hour mark where the premeal insulin has worn off, BGs will continue to rise without any extra input from me. For particularly large or carby meals I can often see this continue long into the night. Sometimes I even add a unit onto my nighttime basal when I am dead sure this is going to be the case (**another non-textbook technique that I can't in good conscience recommend to anyone**).
If I'm eating a high-carb meal, and I do rather frequently sadly, my rule of thumb is "take what you think you'll need...and then take about half that again!" When the meal - and the dose - end up being massive I usually do split it up. I'll take maybe 15-20% of my planned dose (ok, I don't actually calculate percentages, I usually just go "oh let's start with...5u?") "up front," i.e. while I'm still cooking the food, and let that start working. Then just before I start eating I'll take another 30-40%. And another dose just after I've finished eating. And check up on things in a few hours and see if I need more corrections. That gets most of the dose "front-loaded" but also gives me a "tail" that will continue working an hour or two longer than the rest, knowing that the meal will still be digesting then.
Even then I still often find that my BG the next morning will be higher than I would like. But you do your best each time, and sometimes it works and sometimes it doesn't. Sometimes it doesn't make any sense at all!
"Moderate carb" btw is something you will get better at with time. While you were focused on maintaining a strict VLC diet, you worked off of the idea "if it has carbs, don't eat it." And now that you've got insulin, you've been working off the basis of making recipes
, i.e. specific favorite meals and foods that were off-limits for you before and that are NOT designed with carb-counting in mind. Right now you are enjoying eating all your favorite "forbidden" foods that you haven't had in ages without it being a total disaster on your BGs (and I know you don't feel this way, but trust me, these experiments have NOT been total disasters, far from it!) That's an important and necessary thing to do when you get insulin, I think!
There has to be SOME reward to all of this, right?
But admittedly these are not ideal learning situations; these are "INS 202: advanced problems in using insulin" kinds of meals.
Eventually you will come to settle on more of a "middle way" where you are eating meals that are not VLC in nature but that are geared towards an amount of carbs that your body can tolerate and that you can easily dose for. Probably around 30-40g per meal, maybe more, maybe less, you'll find out! In other words, you get to a point where you're familiar enough with carb counting and far enough away from your previous habits of carb restriction that the question becomes not "what can I eat that's not low-carb" but "what would I like to eat today that's around 30g or 40g?" And that's where I suspect that you will really start to feel that there's a benefit to using bolus insulin, because you will get both the increased flexibility with food compared to VLC *and* hopefully see your BGs where you'd like them to be a bit more often. Not every day and not all the time, because sadly, injected insulin just can't hold a candle to naturally-produced insulin when it comes to tight, smooth control. There will always be days that don't make sense because we never have all the information (to say nothing about the ability to respond quickly and precisely) on the outside of our bodies that our pancreases had on the inside. But you'll see better numbers more often than what you'd been seeing once your own insulin, for whatever reason, went more or less Ts-up, and with less draconian measures on the food front needed to achieve those results