Technical 51 mercury disk braks

i have instaled disk braks on my mercury. i have used a duel master cylinder with a duble 7 inch booser. i have 3lb check valves up front &10 lb rear with adjastable valve. i am using dot 5 drake fluid the ssstem is compley free of air. the car stops but i dont like the feal i am told that because the pedel is on the floor its the nature of the beast. is this true or can something i can do to inprove the feal. i would like a hard fealing pedel

 

I only use Dot 4 brake fluid in all my cars changed from 3 to 4 . Have great pedal i stay away from Dot 5 JMO.