the thrust angle (offset angle) is to compensate for torque that the engine produces. as you face your plane, the engine rotates counter clockwise, and the offseting torque goes just the opposite direction. left to it's own, the plane ( with the engine mounted inline with the center axis of the fuselage would have a tendency to pull in that direction. By mounting the engine at an angle, it can compensate for that torque by pulling at a slight opposing angle. . .
does that help?
PS: some scratch built planes of the day had offset built into the vertical stabiliser to acheive the same effect. some motor mounts now have it built in also. . .

Jeff