I sympathize.
I did not have an opportunity to test drive an Air prior to receiving mine (I did have one scheduled, but couldn't make it) and that is my only regret with the purchase process of my "Luci".
I'm 5'11", but rather "rotund" (and in the 55+ club) and I have a difficult time getting in and out of the car without rubbing/hitting my head. (btw, once inside, I absolutely love the car and consider it a "step up" from my S550 that I love.)
I also own a low-to-the-ground ICE sports car, so I'm no stranger to issues w/ getting in and out of a car, but that is not my daily driver and I'm Ok w/ having to do-what-I-have-to-do to enjoy it.
Because of the difficulty w/ entering and exiting, I find myself gravitating towards my F150 (which is great for hauling stuff, but has a horrible turning radius and a bear to park in tight spots).
I've mentioned my concern so many times to my wife (I love this car .. if only I could get in and out of it) .. that she responds by telling me to sell the car (or lose weight
.. which would make it easier, but, even if possible, having seen other 6' folks get in and out of my car, I'm not sure would solve the problem entirely).
So, I'll second your advice. If you are near 6' or taller, and/or "well-fed", I would definitely "try before you buy" and enter/exit multiple times (as you would w/ a daily driver).