Please don't take offense, but I'm going to ask a basic question. Are you only appying pressure to the face of the board, on the outfeed side? If you are apply pressure directly over the head or on the infeed side, you are creating a planer effect, and will never shorten it. My only other comment would be on door stock, I never ever try to work with wood that's already squirly before I start milling it. A 1/4" bow is a lot for a door. For door's it's QS only and I take an initial milling and sticker and watch it. If it's start's moving forget it. Worst thing in the world is to have a door after all the labor to bow because of a piece. Not worth it. I got bit once many a year ago on a project for someone, not wanting to go get more stock. Well what it cost me in the long run to rebuild that stinking door that came out of my pocket, because I was penny wise and pound foolish, was a great lesson. I'd go get a new piece if it were me. But then that opinion and a buck-fifty will get you a cup of coffee.