I don't understand how this works, can you explain more?
I will try.
If you want to ride as economic as possible you want to coast as much as possible instead of brake. So closing the throttle you set 0 regeneration.
Of course sometimes you do need to reduce speed more than coasting and then it's best to recuperate speed as much as possible. So braking through regeneration only.
The regeneration is activated through the brake light switch. So if you pull the handle the regeneration will start when the brake light turns on. But standard this happens (on my bike) after the front brake engages. So it is also braking mechanically.
To separate the mechanical and electrical brake, and to engage the electrical before the mechanical you need to bring the electrical switch out a little bit more so when you pull the handle it engages the brake light/recuperation before it mechanically applies the brake.
If you check the video I made you see that by touching the front brake I'm slowing down the rear wheel because of the regeneration.