Ive got the same set up and only a 23mm master cylinder and the brakes work. It may seem you have bled all the air out, but the problem is when you mount the rear calipers the bleed nipple isn't at the highest point, so you get air pockets in the calipers.

Undo the calipers, lift them so the nipples are at the highest point, and re-bleed, and i think you will find it works

Re-bleed the whole system aswell