Sam; I doubt I can give a real accurate description of the how/why of different suspensions but same ground clearance. But what I get is, the Street Glide has a larger diameter front wheel so some travel was taken out of the forks to compensate for unladen height. The rear shocks are supposed to be shorter, but I think the difference in ground clearance is only fractional.
Something that occurred to me is I see lots of metric bike riders, mostly Sportbikes, that the riders are tip toe at stop. Granted, our Harleys are a LOT heavier, but maybe we put more thought into how much foot needs to be on the ground. You love the S.G. but are inseam challenged, get real good at slow speed maneuvers (especially U turns) and choosing parking and your problem may be negligible. That link HDDon posted looks interesting, probably pricey, but
interesting.