The vertical tracking angle depends on the record height - or, in other words, record thickness. That's correct but the tonearm sits on the same subchassis as the platter so riding a little lower due to record weight (or an eventual clamp) won't affect the tracking angle.
I agree with Chris in that a clamp won't normally be needed unless playing a very wobbly record in which case I would seek to "set the record straight" (sorry, couldn't help it) using one or more of the old methods or use a light clamp to just hold the record down firmly, gripping the center tap rather than using gravity.
Martin