~10 feet from the screen would be THX reference position for movies. At 13 feet, the average person would not be able to distinguish 4K from 1080P. https://www.rtings.com/tv/reviews/by-size/size-to-distance-relationship
I'd do L/R beside the screen, and C behind.
What's your wall colour? Will Axiom do custom colour-matched fabric grills for the M5HP?