I think we must drive differently.
I don't understand how the regen level has anything to do with being able to "coast" more.
When I'm doing long trips (and I do quite a few) I always have ACC enabled and set my speed to whatever is appropriate for the road conditions, typically 100 or 110 kph here in Australia.
The car sits at 100 or 110 and (or "following" the car in front if we're in a convoy situation) with my foot off the accelerator. I can observe the power consumed on the dash and watch it change as the road goes up/down or stays flat. Going down hills it will typically go to zero and often -ive and up hill, obviously increase.
If we're in a convoy the 'flat road' steady state power consumption will be less than if not following another vehicle due to the 'tow' provided by the car(s) in front. Following in a good convoy can significantly increase range. Conversely, being the 'wind breaker' will lower the range.
Regen has nothing to do with travelling at a steady speed AFAIK.
Indeed, people who don't keep a steady speed annoy the heck out of me and I pass them at my earliest convenience, often with a single digit raised