Incorrect, pressure in the system will be the same between master and caliper pistons. However what you mean is it, like many other brakes out there, uses 2 different size pistons.
Why?
Because as the rotor turns, it pulls the pads. The leading edge (edge that hits the rotor first) is pulled...
However shortly after riding due to piston rollback, it will be as if one bled the brakes with the thinner rotor instead of thicker bleed block. This is why we have reservoirs with bladders, as the pads and rotor wear, bite point should in theory stay consistent. However as they approach extreme...
Actually both are wrong to an extent. Modulation is the feeling from initial pad contact to full lockup, and how that power ramps up (or back). Little modulation means it is harder to control little applied brakes to full lock and vice versa. Handfuls of modulation means it is easy to control...