My insulin to carb ratio actually varies throughout the day. I need a little more in the morning and less in the evening. Also, some carbs peak at a different time than others do. For instance, if I eat pizza...I get my biggest spike about 3 hours after I ate it. So if I just take one big bolus up front, I actually get low in the beginning, then I spike later with little insulin left on board to cover it. Trial and error really and I think we are all a little different