I didn't know that their endplate was actually connected to the diffuser....
About the caliper, the mounting location seems to be a carry over from Newey's McLaren days....as far as the relation between brake torque and mounting and other consideration, there are several schools of thoughts out there and all have some reasoning to back it up. Some say you can use the brake's reaction torque on the mount to counteract the forces on the balljoint to lessen the load(and optimizing the geometry of the upright/ball joint better), there are ones that advocate CofG location like the RBR/McLaren, and there are ones that places it in the wheel base to minimize MOI. I am sure there are benefits of each...As far as bleeding brakes are concerned, since most of these calipers are custom to each car, they can probably relocated the bleedport to make that easier. Looking at the RBR car it looks like its not purely at 6 o'clock and that the rear portion of the caliper sits slightly further up, that'll probably faciliate a bleed port in that portion...