How high the rears?

What's the current thinking about mounting rear speakers? Near the ceiling, above ear level, at ear level. Our media room is 14' X 19'. The LR speakers are about 8' apart and 4' from the wall behind them. We sit pretty much at the apex of the equalateral triangle. I'm thinking the rears might be spaced about 6-7' apart.

My wife likes the looks of the ultra thin KEF T301s and I find their sound clean and open, so that's what we're getting. The tweeter will not match the T33 tweeters of the five KEF Reference speakers, but I assume matched voicing is not as important for the rear speakers.

db