I'm experiencing similar problems with an Ag Leader Compass and OntrakIII in my combine set on WAAS.  I set a 5 degree line to cut beans and returning on the next pass I have to nudge up to 60 inches in order to keep the head remotely full or to keep from leaving standing beans.  I've recalibrated several times and done the roll cal multiple times.  Everything is planted with RTK so maybe I'm just spoiled.  I know WAAS isn't repeatable, but it should be better than 5 feet of drift in a single pass.  My dealer talked about bringing out a 6500 globe with a Terrastar subscription to verify that it wasn't an equipment problem, but hopefully I'll be done cutting beans today, so I won't need it much longer.  It doesn't sound that would help either if Terrastar is having problems as well.