I have no experience with combination machines (other than to want one), but... the combination machines that incorporate the table-saw can be heavy,...
Are you creating the pocket hole on the "Right Side" of the joint. The pocket should be created along end grain, so the screw is fastened into grain...
One of the writers at FWW did an article with a similar plane cabinet that had the back at an angle where the top portions of each frame had a small...