I had a very similar issue when I went from B&W to Thiel speakers. The vocals in the center image always seemed soft.
In the end I never fixed it and came to the conclusion that it is just that the Thiels have a wider dispersion of the mids than B&W speakers (especially the smaller ones,803,804 etc) and that B&W speakers have an artifiacally focused midrange. But setup can help a bit.
I could never put my finger on it until I had a demo with the Sophia 3, thiel 3.7 and B&W 802D all in the same room for an A/B/C demo. The Thiels had the worst case of this issue (diffused vocals) but the best lateral dispersion. The wilsons sat right in the middle of focus and dispersion and the B&W had a laser focused midrange.
After a long demo I came to the conclusion that it is a combination of lateral dispersion and driver integration. The B&W sounded the most fake but also had the most 3D image maybe due to poor driver integration. The vocals stood forward, and highs stood out and the bass filled the room and left a very 3D image while being somehow unnatural.
Also what I found that day is that the Sophia is pretty setup critical. Of the 3 speakers it was most effected by the seating height and speaker angel where the Thiels are least sensitive.
So on to solutions. Getting speakers wider and more toed in will help but it sounds like that is not possible for you. With wilsons one thing that could work is tilting them forward as much as possible to get the mids range/tweeter more pointed directly at you. Since the Sophia's head is not adjustable the seating distance window is a lot smaller than the other wilsons.
You could always try a taller/short seat too in order to get the sweet spot right if you limited in you speaker position. I thought the Sophia 3 sounded best with a 10'-ish triangle (every side 10') and tilted forward using a standard couch to sit on.
In the end I never fixed it and came to the conclusion that it is just that the Thiels have a wider dispersion of the mids than B&W speakers (especially the smaller ones,803,804 etc) and that B&W speakers have an artifiacally focused midrange. But setup can help a bit.
I could never put my finger on it until I had a demo with the Sophia 3, thiel 3.7 and B&W 802D all in the same room for an A/B/C demo. The Thiels had the worst case of this issue (diffused vocals) but the best lateral dispersion. The wilsons sat right in the middle of focus and dispersion and the B&W had a laser focused midrange.
After a long demo I came to the conclusion that it is a combination of lateral dispersion and driver integration. The B&W sounded the most fake but also had the most 3D image maybe due to poor driver integration. The vocals stood forward, and highs stood out and the bass filled the room and left a very 3D image while being somehow unnatural.
Also what I found that day is that the Sophia is pretty setup critical. Of the 3 speakers it was most effected by the seating height and speaker angel where the Thiels are least sensitive.
So on to solutions. Getting speakers wider and more toed in will help but it sounds like that is not possible for you. With wilsons one thing that could work is tilting them forward as much as possible to get the mids range/tweeter more pointed directly at you. Since the Sophia's head is not adjustable the seating distance window is a lot smaller than the other wilsons.
You could always try a taller/short seat too in order to get the sweet spot right if you limited in you speaker position. I thought the Sophia 3 sounded best with a 10'-ish triangle (every side 10') and tilted forward using a standard couch to sit on.