It sounds like the servo assist isn't, but two not working is very odd.
Master cylinder bore will affect the mechanical advantage of the system (big bore shifts more fluid, but the area is bigger so less fluid pressure for a given pedal / lever force; small bore is higher pressure but less flow - which is what disc brakes need). A way round it is to change the lever ratio, so that there is more of your bit of the lever than the master cylinder gets (if you follow). The Milner site shows levers with a ratio of about 10:1?
However, as your servos are remote, they only work on fluid pressure anyway, so they should be doing some good ...