From what I have been told eons ago motability and manufacturers agree on the price of a particular model. Motability expects to get a certain amount of money back when the car is sold after end of lease. They look at historical used values and if that particular model is sold less than what motability expects then the difference is covered by the AP. Of course there are other factors affecting APs. Motability and manufacturers are pushing EVs by lowering APs on some models and dealers offering further discounts.