Thanks, but with a 46/30T crankset and 34T or 36T cassette, I am as low as I can go with Ultegra Di2 (officially the rear derailleur is limited to 32T).

My main point is the difference in torque should, at the maximum point where the force is perpendicular to the lever arm, should only be 4.3%. So I think something else must be going on.