Regen on AWD model

I think it has to do with load distribution and the fact that vehicle momentum during braking leans forward and puts 60% to 90% of the braking load on your front brakes and regeneration is a form of braking.

 

The battery size is the limit of how much braking force it can apply. It can only take in so much charge at once. With most of the braking done at the front, the system will apply most of the regen braking there. Plus, the system design was developed for FWD. Braking from rear is likely more for keeping the car straight as opposed to stopping.

The SUV can have a heavier load or trailer. Rear braking sees more use with that. Toyota could have set the regen braking to always apply some to the rear for that reason.

Then we are going by what the dash display shows. We have to take it on faith to be showing that braking is happen, and then it doesn't show degree of the force applied. The Prius and Rav4 could both be generating the same level of rear regen braking all the time, with that base amount not being high enough to register on the Prius dash.

 

For gentle braking, there should only be regenerative braking and no friction braking. Since both front and rear brakes are used for braking, I would think that for gentle braking, there should always be regenerative braking on both front and rear axles. There would have to be more braking on the front than on the rear like it is the case with friction braking. But then, the non-AWD Prius and Prius Prime don't have a rear motor and no rear regenerative braking; so, perhaps what you are seeing makes sense. I don't even know how often the rear motor is used for propulsion.

If you are really curious, spend a few bucks and download the new-car features manual from Toyota Technical Information System (TIS).