Bookvault sizing?

I’m trying to get a cover template from Bookvault for my cover designer, and as a US author, I’m really confused…. The sizes don’t seem to correspond to normal American print sizes. I’m trying to end up with 9×6” (hardcover), and the closest thing I can find is the US Royal size, which has cover measurements of 229mm by 152 mm (9.015748in by 5.984252). I’m concerned that might not be close enough for me to use the same text files as my KDP paperback, though….

I’m also open to looking at printers other than Bookvault, but I’d heard good things about them for hardcovers with dust jackets. I’d appreciate any help anyone can offer!