Possible cause is the angle of the wing. On the High wing Cessna aircraft the aircraft is rigged to fly straight and level by adjusted the rear spar mounting point this is a bolt which is fitted through an offset (eccentric)bush, rotating this bush lowers or raised the trailing edge of the wings, so if you have an aircraft that does not trim out level the engineers can raise or lower the trailing edge thus affecting the whole angle of attack on that wing to compensate, It is possible they are both set slightly different. and hence you are seeing the difference in the angle on the pitot tube.