Read thru Stoptech's website. They offer a lot of technical detail about setting up braking systems - especially as it relates to MC sizing. You need to look at your MC bore sizes, caliper piston sizes, and measure your pedal to get the ratio. They have formulas there for zeroing in on it. I have not used these formulas to experience their effect, but I plan to with my current project.
StopTech : Balanced Brake Upgrades
"1) Line pressure can only be increased by either increasing the mechanical pedal ratio or by decreasing the master cylinder diameter. In either case the pedal travel will be increased."