I've ordered a tubus rear rack for my Peregrine today, looking at the pictures on the Singular site the raised mounting points look great for disc brake clearance but do they mean the rack is going to sit much higher than usual?

The rack in the singular photos (nitto I think) sits a long way above the brace between the seat stays needing an unusual front mount. Or is that normal (I'm not a rack expert) Photo at:

Most racks can/should be mounted on the upper bolts near the seat bolt. There should be enough adjustment in the arms to fit just about any bike, and if not you can usually bend them or use some different arms to make it work.

you can also get different length arms from tubus

There are bosses on the side of the seat stay which most racks should attach to. That particular rack is a Velo Orange and doesn't have the 'normal' method of attaching the front mounting point, they are essentially designed for bikes with caliper brakes. A tubus rack should be fine. Which one do you have? Single mount or dual mount? Dual will be better and should go straight on to the upper bosses on the seat stays.