I did early on with a pair of 3.6s have tweeters out... I felt that in my tiny space, with tweeters out, I lost a bit of center focus.
I did ultimately mess around with room treatment, presumably which would have minimized "early" reflections from tweeters out. However, when I first experimented with tweeters in, I just felt that I got a razor sharp center image and less so with tweeters out. I preferred this even if it meant sacrificing a bit of image width.
And I felt that in my case image depth was a bit better... tweeters in.
Having said all that, I am fairly regularly tempted to swap back to tweeters out just to have a listen. one of these days.