Probably stopping better because the rear's are actually working with weight. Your pedal will travel more as the fronts alone can't stop it before the rear's kick in.
I have seen over-sized wheel cylinders, but have never heard from anyone who tried them.
I saw those oversized wheel cylinders when looking at the rear disc conversion companies websites. Turbine Doc's company specifically. Give em a shot, they weren't much cake.
Are they well adjusted? Either jack it up and adjust them, or go into a parking lot and roll backwards fairly quick, and snap the brake pedal hard about 10 times and see if its better pedal.
Never liked drums..... audo adjust? yeah right.