Based on how @Karthik ruled in the similarly size-limited Bank Shot VEX IQ game a couple of years ago, I’m certain that what matters is the square on the ground. In Bank Shot, if you fell over to gain an advantage, your height was ruled out of compliance with the limiting rectangle. So you could get a DQ. If you fell over inadvertently and it didn’t affect game play, then you would be warned but not DQ’ed.
Here’s the thread from a couple of days ago where I discussed it: