do you mean that 8260 has a better soundstage?
Keith can correct me if I'm mistaken, but I'd say No, he's not saying that. He's saying the larger Ones are more enveloping when you're listening from more than 2M away. But that's only one aspect of soundstage. The 8351s (which I own) throw out a first-rate soundstage - very strong and sharp phantom center; excellent width and depth; and very decent height for a standmount.
I haven't heard the 8260 or 8361, but I listen to my 8351s from about 3M away and I would agree with Keith that I do not usually feel "enveloped" by the sound when playing them. Based on some brief experimentation with higher volume playback, I believe that if I turned up the volume further and played them really loud, I could achieve that envelopment, at least to a degree - but that would be way too loud for me. I would also say that a feeling of envelopment is akin to (or at least related to) the idea of "pressurizing the room," which takes a fair amount of volume if you are listening in a room that's large enough to be sitting more than 2M away from the speakers in the first place.
In my case envelopment is not an issue as it has never been high on my personal preference list for sonic enjoyment. In fact, I actually usually prefer to be "looking at" the music because when I close my eyes it makes me feel like I'm sitting in front of the musicians who are playing on a virtual stage; it's like I'm sitting in the 2nd or 3rd row or something. In fact, I had considered the 8361s quite seriously and in the end decided to get the 8351s, thinking they'd be adequate for my needs - and I have not regretted that choice.
But if you want to be enveloped and you are listening from 3M or so, then I would agree with Keith: listen to the 8351s before purchasing because you might not feel that envelopment at that distance.