If you want more braking you need to do the opposite on the master cyl, go smaller or alternatively go bigger on the caliper or slave cyl pistons, works the same as sprocket ratios, hydraulic pressure ratio.
The smaller the actuating piston(brake lever) is with relation to the reacting piston(caliper or clutch), gives you more power on the reacting piston with less effort on the actuating piston, but less travel on the reacting piston & more on the activating piston, but seeing as a disc brake caliper only has to travel a fraction it does not matter so much & the gains on braking force with less hand effort are a big plus.