I'm a bit stuck for position with the speakers as you can see there is a pretty large cabinet between them. They are not actually as close to the corners as they may look (appx. 70cm each way) The cab was custom made for me and very expensive, so I am loathe to get rid of it.
however I have moved the speakers out and in front of the cabinet to see how much difference it made. The answer surprisingly little. Mid range and treble stayed pretty much the same as far as I could tell. There was a noticeable change to the bass, although it was different it was not either better or worse, possibly just a tad tighter. I put this down to the tuning ports (in the bottom corners) having a bit more air about them, but it certainly wan't a night and day difference.
I've not had experience with other omni speakers so can't really say how others fair but to my ears they seem to cope better in a variety of positions than any std box type I've known. You do get lots of reflected sound but then that's the whole point of how they work. Other types of speaker tend to fight against reflected sound. These seem to work with it and to my ears the result is very pleasing indeed.