Just noticed this; on an account that has none of the High Elf items, the set's 65% off at 931 H. I own 8 of the 24 and my discount is . . . 66% off at 893 H. I got an Amazontwitchprimedropthing for most of these items, the settlement decorations and the two weapons. I'm guessing that must be something to do with it. Doesn't quite explain the addition of merely 1% to the discount for owning the cloak via Reda's Rubbish.
Previously there was a somewhat-worse issue with the Berserker items. I think this is the same sort of thing. For that one I had all but the tattoos via the preultimateorderdeluxeversion.