Hi Flavio.

I assume that -2 degrees places you engine into right thrust. That's normal to counter the severe left torque of the engine. That means that looking from the rear of the plane, the engine will point a little to the right. That's normal. All my singles have right thrust. Now look at the firewall from the front of the plane. The engine will be pointing slightly to your left. Therefore the the rear of the engine mount must be set slightly to the right of center. (looking from the front).

If you want to apply down thrust. This counters a plane with a flat bottomed wing from climbing when power is added. The calculation is the same, but now the engine will point downwards and the rear of the engine mount must be slightly higher that the thrust line of the plane.

Good luck. I am glad I could help

/colin