Hi John,
You have it right! Boats sail faster to windward with the rudders loaded, carrying some of the side force equal and opposite to the sail side force. The windward rudder in this situation which in moving into and out of the water vertically as the windward hull moves up and down will stall if it has the same angle of attack as the leeward rudder which is totally submerged. Reduce the angle of attack of the windward rudder a couple of degrees, rudder toe-in, and the windward rudder does not stall as it moves in and out of the water vertically and as the boat travels ahead.
Good Sailing,
Bill