Make sure you separate cable-friction from caliper-friction. Disconnect the cable from the rear-brake and pull on the inner-wire and alternate between pulling it versus squeezing the brake-lever (flossing the inner-cable back and forth). Due to the length of the cable-run, housing-compression and friction, you can never get the rear-brake as crisp as the front.

A lot of calipers have adjustable spring-preload. I typically set the front-brake to low-preload and the rear to high-preload.