Mike:
Because of the lower brace height with the longbow hand placement on the grip is more critical, try rotating your grip so the large knuckle of the thumb is more inline with the center of the limb.
This will do several things, it straightens out your wrist, which in turn moves the forearm out of the way. When the bow is placed in the web of your hand it pulls your forearm right into the bow string. By rotating the hand like I said, you will also not torque the bow as much upon release.
Bob