RE: Pusher Prop Thrust Line Offset from Datum Line
There is a nose down pitch that is induced by the moment or torque of the thrust force times the distance of the perpendicular to the CG.
For the airplane to be stable in horizontal flight, the sum of the moments and forces respect to the CG must be zero; hence, the moment that is induced by the thrust must be balanced by an equivalent pitch up moment.
Generally, that balancing moment is achieved by a combination of several gravitational (from CG locations) and aerodynamic (from airflow) forces and their respective arms.
Downthrust and upthrust angles tend to reduce the arm of the thrust.