I am experiencing virtually the exact same problem as described in the initial post of the following thread:
My water level has to be a couple of inches above the midline of the skimmer plate just to prevent the pump from sucking air with the vacuum plate on. I'm thinking of maybe using a PVC elbow and feeding the vacuum hose through the skimmer opening. Has anyone else encountered (and solved) this problem? The problem was never solved in the thread mentioned above.