That's normal for XD and XDr. Hope does the same thing. been like that for a few years. XDr 12 speed uses 11-speed spacing between gears so it needed a bit more room - just shy of 2mm as it would happen. I am assuming 13 speed comes about by SRAM using a narrower-than-11-speed spacing on the XDr driver. Certainly, it's possible that if/when SRAM releases mountain 13, they need to go on XDr to get every little bit of room they can.