I guess that's the "secret to successful D management" - the serving size.
If I understand correctly,
if you have a certain range of carbs per meal and if you stay close to that number, the carb ratios and bolusing works well. If you exceed a certain number of carbs, the ratios no longer apply. Insulin dosing is not linear. For example, suppose your normal I:C ratio is 1:10 for meals up to 30g carbs. If you were to eat 90g carbs, 9 units of insulin may not work. Is this related to insulin resistance? or is it possible that our individual bodies are more "comfortable" (or can better handle) with a certain amount of carbs per meal? And this varies from person to person. For example, @Jen, 80 grams of carbs breakfast may not be what your body naturally feels comfortable despite using the appropriate amount of insulin. Another person may eat 80 grams for breakfast daily and use insulin and it would work for that person.
If I keep my carbs below 20g for lunch and dinner, my post meal BG is often between 100 to 120. If the protein portion of the meal is "too high", then I experience a mild increase in BG at around the 3, 4 hours, BG can rise to about 140's. The next morning fastings are generally around 100. On the other hand, I've noticed that when I eat about 20g carbs for dinner, the bedtime BG is between 100 to 120 the next morning fasting BG's are somewhere between 80 to 90. It seems like everyone has their own "sensitivity"- the carbs level above which too much effort would be required to correct, correct again, and possibly again.