When the thrust line is above the center of drag for the model you need to compensate for that. On the first version with the pylon the motor needs to use a goodly upthrust angle in order to avoid the nose down issue at full throttle. Sometimes even as much as 7 to 10 degrees.

On the rear mounted version in the second picture you're thrust line is down closer to the center of drag but now your prop is behind the CG. For this setup you want to use some upthrust angle so there it lifts the nose at full throttle. I'd start with about 2 or 3 degrees and alter if from there for more or less upthrust. And in this case, just so we're all clear, upthrust for a pusher model is when the prop is more forward at the top of the circle than at the bottom and the axis of the motor is angled down as it extends to the nose. The same angle for a motor and prop on the nose would be DOWNthrust but because your prop is behind the CG it's now UPthrust. Clear?