UW -

My daughter is about 5' 8" and yeah the rail is probably long enough for her to go fully extended. We did play around with a more extended left hand grip, elbow raised and less bent, wrist position modified - and there was still plenty of room on the 12" rail at that point.

I get what you're saying about rail lengths. I wonder how much of the longer-length mindset has come from decreasing the rail outside diameter. Its not just weight at that point, it's how your wrist and hand connect with the rail and how that relates to elbow position. I'm sure there are some fancy biomechanical reasons that some of these styles work comfortably for some rails, but are clumky with others.