Center image on left side and don't know why

Just experiment with moving 1 single speaker foward or back to get it to lock in, that will likely fix the symptoms and may even be the cause....

You also want to make sure the recording you are using for reference actually has the vocals center stage. Many recordings, especially operas for instance, will place the vocalists all over the soundstage, for example, from standing just a foot inside or outside the speakers, to a few feet off center and dead center, actually anywhere inbetween the speakers and even outside the speakers, of course if your gear (and room) is up to that task.

From my experience, which goes pretty much along what is in the 12 page speaker setup manual that comes with Von Schweikerts (and similar SHOULD come with all big buck speakers, but many don't have more then a page of help):

-Toe in should be used more to lock in the 3D image, to obtain the most depth of the soundstage, the most body to sounds. The best way to do this is with pink noise, getting a phantom ball with 3 dimensions floating center stage much lounder then the faint fuzz from the speakers directly. Also worth note is that both speakers do NOT need the same to in angle, one can even be much further toe'd in then the other in order to create the best 3D image.

-The speaker distance relative to the rear wall (front/back) I would use for the 2D lateral imaging, locking in the center image, and the distance from the rear wall will affect 3D images, making the sound flatter if the speakers are too close, also greatly affect bass performance, of course.

-The speaker distance apart and from the side walls will greatly affect vertical imaging (rubber-band effect). Going too far apart and the stage will squish down, so keep moving out until the stage squeezes down, and don't hesitate to go a good 10ft apart or more with most speakers, even 15ft is not unheard of with great speakers The imaging as such across a huge stage is extreamely impressive! Personally, I can't stand to listen to speakers that are not at least 8-10ft apart, the overlap and lack of image specificity just annoys the heck out of me (yet, for whatever reason, 99% of dealers will set speakers 5-6' apart, where they sound like crap, and its hard to assess the virtues and vices of the gear...!).

This is just general info and there's much more to it, especially regarding room interactions (which make up for at least 50% of the sound!). There are plenty of books on the subject and many websites with info you can easily find, very good reading.

That's another problem I was thinking of but forgot to mention: Many speakers have a "head-in-a-vice" sweet spot, move your head an inch or more one way or the other and the magic is gone, the soundstage collapses. Such is the problem with the majority of time-phase aligned speakers, the sweet spot is the only sweet spot, sit anywhere else in the room and the sound is just mediocer at best, any other person listening is not getting 1/4 of the magic, although there are a few speakers that can offer a sweet spot as big as a sofa and the music will still be stunning even in a different room entirely....btw, did I mention how much I like Von Schweikerts? :o)