I'm happy you wrote this. Because what you wrote earlier "Regen provides such miniscule charge that it's practically worthless" was just nonsense in my opinion. Come to Switzerland an ride some mountain passes. Last Saturday I gained 10% riding downhill the Stilfserjoch ....
I thought Stilfserjoch was in Italy. Anyway, my personal preference is the backroads of France, and the Pyrenees mountains.
The physics say that you'll always use lot more energy going up the hill than you can possibly get by going down. How much you can recover depends on many factors. Most of them add on top of each other.
So the 90% converting-stored-energy-to-electricity-efficiency of the batteries (actual percentages will vary, these are examples to aid in visualization), added to 90% motor efficiency while riding (81%), added to the 90% efficiency of the belt, (73%), added to 90% the road to tire resistance while using power (66%). This is for riding, now lets turn it around for charging. The 90% road to tire resistance (59%), added to the 90% efficiency of the belt, (53%), added to 90% motor efficiency while charging (48%), added to the 90% converting-electricity-to-stored-energy-efficiency of the batteries (43%).
So this example gives 43% max possible energy recovery, without taking into account wind resistance (dependent on speed, doubling the speed gives you 4 times the wind resistance) while covering the distance. This will depend on the road, how much you are slowing down for various obstacles and number of said obstacles, and the vehicle.
Most of the energy is being used by actually covering the distance. So IMHO you'll get more effect on range by dropping the speed by 2-3 kph or always ride with the wind in your back.
If you want more scientific explanation, see here
https://www.sciencedirect.com/topics/engineering/regenerative-braking,
or maybe here
https://www.coltura.org/electric-car-battery-range "regenerative braking only adds 10-15% more range with city driving and a negligible amount with highway driving"