I want to write a smart post on this topic. But until I can put it together, the simple idea is this:
For most PWD’s, their insulin duration is 3-6 hours (varies based on infusion, activity, etc).
And for most people (diabetic or not), meals take anywhere from 1 hour to 2 hours to metabolize (varies based on the type of meal, fat, gastroparesis, etc.)
The general pharmacokinetics & pharmacodynamics for insulin (again this varies for everyone) is that half your dosage is used in the first hour. The remaining duration is where the rest of the half dosage is used, hours 2-3 or 4.
So the reason for the double - if food is metabolized in half the time as your normal duration, and normal absorption is 1/2 of the total in the first hour…doubling matches it better. The remaining insulin for the the next few hours is extra, that needs more food. But at least your dose matches your first few hours of food metabolism better.
In simplest terms:
Rather than waiting for a high to come down for 2-3 hours, you take more insulin at mealtime, and eat more food an hour or 2 later.
That’s my quick explanation. We should expand on this a bit as time permits.