During hard braking will twist the toe board where the brake master cylinder is located, and this results in decreased brake pedal effort.
To improve the brake feel further, CUSCO recommend the master brake Cylinder stopper. What this is is a bolt-on unit that attaches to the back of the master brake Cylinder piston and the suspension tower to eliminate movement on heavy braking. Brake feel will improve as the master Cylinder does not flex anymore.

Cusco brake stopper installed on GDB STi today. Below are the pics.