Audiotroy's point has come up before. Years ago over in Stereophile forum, I had made a comment on the LS50s and he argued they had an issue at high volumes due to the tweeter limiting excursion. This would extend to any speaker using the UniQ driver and even showed it in a measurement plot they provided.
I am not a Kef dealer or expert and can't speak to it. Only that I have heard it raised as an issue previously. I will tell you that Vivids will not have this problem. And, even though you would think it would be an issue, near wall placement with those side firing woofers is not an issue. I have tested it on my Kaya 45s. I am not sure how or why it works, it just does.