how to determine overlap

I've been reading this theory that different areas (scruff vs flank) not only absorb at different rates, but the location can also affect duration (and that would affect overlap) (consensus seems: scruff=slower onset and longer duration; flank=quicker onset but shorter duration)

But, how does one determine overlap in the first place?

 

You'd need to collect sequential blood samples at defined times (ex hourly) and test the insulin levels.

You might infer it from glucose levels.

Regardless of method, you'd need to keep the food intake on a strict schedule when attempting to assess this.