It's a non issue for me the room has a vaulted ceiling and some stone walls; so is not a 'cuboid box'; so no isssues as far as I can tell.
I bought ATC's on the strength of their accuracy because I had become involved in a recording project with a Grammy winning producer/engineer in the USA...
Newbie alert.
Here's my ATC SCM40 actives which I recently bought. It took around 6/8 weeks for ATC to build them from placing the order. I just use an Innuos Zen Mk2 server with an M-Dac+ (integral volume control and headphone amp) and these.