I ride a 140 Mako. I think I have it set up well for me, on a normal day I can go out and not have pain.
You can't get much better board for knees in chop than a Mako 140, I have a 140 and a Shinn Gintronic and I have knee problems.
For me less duck in the stance helps out, but if it is the duck in your stance nothing will solve the problem like going directional (you don't have to go strapless, but it would be even better).
Which knee is causing the issue and on both tacks or only a specific side?