My speakers are almost agnostic when it comes to placement in the room however toe-in has revealed where the optimal angle of attack/imaging is achieved.
I've got the ProAcs 56 cm (rear of cabinet) from the front wall, 100 cm from side walls, 250 cm tweeter-tweeter apart, 290 cm from speaker to ear, almost an equilateral triangle.
Once I got the speaker placement about right in the room I started spending days on getting the toe-in right to get a balance of soundstage and imaging, soundstage being the approximate dimension of perceived venue/recording space and rough idea of the instrument/performer position within the space between/behind/in front of your speakers. Getting the imaging right is much harder for me because getting wonderful deep/wide soundstage can often be at the expense of imaging - to little toe-in and a vocalist sounds like they have a metre wide head although the soundstage depth can be impressive it's also rather diffuse, like a broad brush stroke approach. Too much toe-in and the soundstage becomes much tighter and you can also lose depth and width however imaging could be much improved as the performers come into sharper focus/highlighted in the soundstage.
One thing that is also very relevant to both soundstage and imaging is where the tweeters 'cross over' (axis?) In front, directly at ears or behind your ears, Personally I've never understood why tor-in should be so severe that the cross over/axis is in front of the listener, for me this just creates a totally flat two dimensional soundstage.
My ProAc's have offset tweeters that are 80 mm from inside cabinet wall and this does decrease baffle diffraction that can assist in room placement, the tweeters can be placed inside or outside depending on wall boundary - I use mine with the tweeters on the inside.
My tweeters axis is probably a couple of metres behind my head so the toe-in angle is quite small but with the combination of boundary placement, distance from speakers etc I get a lovely deep and wide soundstage and in front of the speaker plane - this is important for me because a lot of setups I've heard the soundstage is only on the speaker plane and behind the speakers, with my setup is really does have a near perfect combination of soundstage and imaging, this is the icing on the cake for me because I can sink into the music and stop thinking about accuracy, recording quality, less than perfect mix or other 'hi-fi' pretensions.
There are so many recordings I have that I literally gawp at the cavernous soundstage yet I can pick out an individual drum position on the kit, where backing vocalists are stood, the height and width of a 'live' studio and a venue - man I can't get enough, I don't care if its artifice, my imagination or a trick of the engineer as long as I can sit back and be immersed into the music.