I don't think hieght really has any real connetion to the size or depth of a womans vagina. I've heard tall women complain about a partner they considered "too big" I think the tallest woman I've slept w/ was 5'9" and she also had the tightest pussy that I ever felt. Anyways I think there may be some truth to a large woman not getting the full length due to a large belly and or large thighs in the way, as I said in a previous post a new position can make a world of difference. One position you may even want to try for "minimum penetration" is tell her to close her legs while you rest your legs on top of hers and slide between her thighs, penetration may be difficult to achieve in this position but it can be done, I've had lovers say I wasn't as deep in that position, so if she's unsure if she can handle all of your manhood, this may be a great position to try first.