I actually had a higher trap running less boost also. Why might you ask? Traction. Try getting a great ET/time when you spin your tires all the way through second feathering the throttle and part of 3rd . The only decent part of those runs was my top end, and let me tell you, I was making waaaay more torque at 24 psi than you are at 13.

Edit: I should also mention that I left my 50 lb sub in the back, along with assloads of tools, and had a 300 lb passenger in the car at the time (wasn't seriously racing that night).