Vandersteen 2Wq corner placement?

I have a pair of 2Wqs, one in each corner just behind my mains. The 2Wq manual suggests if you are using just one 2Wq that it should be located somewhere in the plane behind the mains, especially if your mains roll off before 40hz. The higher this roll off occurs the leaner the mains will be due to the 6db high pass filter used with the 2Wq, and the more likely one 2Wq will be identifiable if used in a corner. As Bigtee said there are many adjustment possibilities with the 2Wq that may help to minimize this. You won't really know until you try. I had a Rel Stadium III prior to the 2Wqs. The Stadium III was very good in my setup, but it did not offload the mains, and it did not provide stereo bass (unless you buy two). My experience is similar to Bigtee's in that the 2Wqs outperformed the Rel, especially with the M5-HP filter. You can buy two 2Wq subs and a M5-HP filter for about the same price as one Rel Stadium III. While I think the Vandy is a better value, a Rel Strata may be a better option in your situation.

I also have a pair of 2Wq matched to MG 3.6R. One of the subs is in a corner directly behind a speaker. The subs are properly intergrated and cannot be localized. I also have a V2W that is placed in the back of the room for HT.

I think it will be kinda tough to get a single sub in the corner to integrate properly. The only way to know is try it. No two rooms are alike. It really needs to be between the speakers on the same plain. I think you will get a little bit of directionality(you will be able to hear where the sub is located.)
The 2wq has lots of adjustment possibilities. It is always possible to get a combination that will work.
I use a pair of the 2wq's(one in each corner)It is an excellent sub for music. It is very tight, quick and dynamic. A lot of people are on the REL bandwagon. In direct comparison, the Vandersteen is a better performing sub in my system. There are some very good design reasons for that. The idea here is not to "Hear" the sub but just give you the lower octaves of music when called for. The Vandersteen does this extremely well. It is also extremely well built. I personally think it is a lot better buy(as in more for the money) than many other subs.
With that said, the REL offers some unique adjustments that may help you in your particular situation. Paradigm also makes a couple of excellent subs and some others as well. You will really need to experiment to find what, if anything, really works.

The corner behind the speakers is the best place for your sub.