L is pretty close to max regen, you might be able to get a tiny bit more by padding the brake ever so slightly, but too much you dig into the friction pads and cause more loss than good to heat (using the brake pads).
One thing about L vs brake is that the rear lights don't come on which causes 2 thoughts:
1) L does not warn people behind you you're slowing down, so be careful with this.
2) Using the brake pedal lights up and brake lights and also eats into your range by increasing the draw on the battery. You can see this in the energy meter. Its a small amount, but it could mean the difference of a mile range if you use the whole battery.
So with that said,
1) use L at night when there is no-one around to even see the brake lights when you need the absolute most range.
2) if you have to use L with traffic, pad the brake pads lightly to light up the brake light. Just enough until you see the regen circle around the battery indicating the brake lights are on.
3) While you can, don't use L all the time "just because". It has its purpose, but don't substitute it for the brake otherwise you'll cause alot of wear and tear on the shifter not sure if it will be an issue or not but many times if not necessary I just relax and drive the car normally instead of shifting all the time -- like for the little trips around town where I have plenty of battery to spare.