I'd try changing powder or charge...In my Knight Disc I shoot 90grs of Goex FFF and the same ShockWaves, my hunting partner's American Knight is sighted in with 100grs of Pyrodex R-S and a 250 Shockwave...

Now, I do the load testing and sighting in for several different buddies...With these two guns and loads, I sight in 2 1/2 high at 100 yards and the bullets hit about 2 1/2 low at 150...I can keep all shots within 4 inches at that range, which is within 2 inches of the aimpoint...In fact, I usually tweek the initial sightin with a scope sighted inline at 150 and then back in to 125, 100, 75 and 50 and give a target to the owner...

As said, you're close and many guys are happy with that...I just love to shoot...