I have some resawn panels of walnut that are about 13" wide and around 1/2" thick. They cupped pretty badly, and fairly immediately when resawing. I've wetted the concave side and they will flatten out. Great right?! but once they are flat and I put them up on stickers and weigh them down, they keep going back to their cupped state within a day or so. I've repeated the process multiple times now and things don't seem to be improving much. What am I missing? Is there something else I need to be doing after they go flat to help them STAY flat? I hate to just trash the whole bunch of panels but right now there's no way they will stay flat in their frames.