Another voice calling for ditching the back-scabbards and storing of weapons there. They are just stupid and lazy and look awful. Ever tried drawing a four-foot sword from over your shoulder? Even an orangutan would struggle.
Quite. And it's unnecessary: I can yank a hand-and-a-half out of an ordinary belt scabbard in spite of being neither particularly tall nor in possession of very long arms; anything bigger than that would go on a cart or something.
When it comes to realism, back-scabbards are up there with "swords weigh 40 lbs and claymores are 8' long!"