Check to see if all the caliper slides are moving freely, if one slide is frozen then the pads will wear unevenly this will cause exsesive piston travel and flexing of the caliper. The volume of the calipers compared to the master cylinder is probably about 10:1 so it takes alot of pedal travel to move the calipers a very small amount. I see alot of cars come into my shop with this problem. Also be sure to use a pure silicone grease to lubricate all your slides and hardware, if you use a petrolium based grease it will will damage ruber seals and bushings. Good luck.