> the engine brakes are also applied by the system, from 10 psi or more depending on the brake pipe reduction,

Having used blended braking for quite a while, it would be less confusing to say that 10 psi is retained in the brake cylinders when the dynamic current builds up beyond a certain level, and the amount of dynamic braking current depends (somewhat crudely) on the amount of brake pipe reduction. The entire intent of blended braking is to rely more on the dynamics than the air brakes, so that 10 psi (or so) never increases until DB fade. Blended braking doesn't use extended range DB. You can also indulge in blended braking with freight trains, but it must be done manually.