VTF only changes when you hit a warp because of inertia - the same reason you feel more force (and then less force) when driving over a bump in the road. It has nothing to do with the angle of the tonearm. The only change in the vertical force vector is as the stylus is raised vertically is due to the change in gravitational force as you move [mm to cm] further away from the center of gravity, and therefore the force of gravity changes. This is why it's called "Vertical" tracking force - vertical states the direction of the force vector.
