The point where the bleeder hole goes into the piston bore has to be the highest point on the caliper. I have an after-market caliper, and have to rotate the caliper on the axle to get the bleed passage in the right position, as well as have the bike leaning to the left. It looks like the F caliper has the bleeder off-set from the center of the bore to compensate for the rearward tilt of the caliper, but it may help to raise the rear a bit? (without seeing the orientation on the bike, it's just an educated guess...)