While the geometry of the "floor loading" in the C-5 case, certainly dictated the high-wing configuration; do NOT discount engineering fashion on the T-tail. Every airplane in the late sixties, save the 747 was T-tailed. Rear-mounted engines also was an influence in planes with them, but another fashion that has gone by the boards.
Back to the C-5, if I could have changed anything thing on the plane--a low-mounted tail would have been numero UNO! De-icing the beast was difficult at bases with the equipment (very few, only MAC bases) or impossible elsewhere. Not many airports have de-icing equipment with 70 foot reach, other than the terminal window-washing stands. Bloody pain. Good place to watch an airshow
crew---
commanders!!
The wing anhedral was definitely a design requirement to suppress the strong stability caused by the high-wing, check out the C-141, B-47, B-52 and all the Russian military freighters. Tupolev Bear, also.
GF