Are you using cold butter? Like borderline frozen butter?

This is correct, it's something called solidity, ratio of number of blades, diameter and chord length. Generally the lower you go the more efficient, though there is some lower limit.

Sure makes sense, I'm American so there are different considerations here.

I'm also not against this, just answering the question. The higher off the ground the panels are, the more it costs. Its a cost benefit calculation.

Just the first car that came to mind as a not very tall vehicle most would be familiar with. No other reason.

Cost.

The higher they are off the ground the more steel you need to keep them up. They are more subject to wind loads. They are also more difficult to service.

Then you ask how high to make them. Tall enough for a Tesla, a crossover, a lifted pickup, a semi, taller?