I wouldn't doubt that the 2 factors conspire together to give the better ride. It's years since I ran dedicated winters (don't go up in the mountains as much, and it almost never snows in town), but when I did, I ran Blizzaks (non-rft) and those had a very heavy, grindy feel reminiscent of current all-season run flats (though they were a tad softer) which were on 18's with about the same profile as 19's on our F10's, which I imagine would have been damped by a higher sidewall. (Was on an Audi A6 years ago, pre 2008). Tires have improved a lot so my anecdotal evidence is suspect, but... what I'm really trying to say is it seems likely that wheel size a combination has something to do with it.
All this at least has inspired me to give this a shot
Now if I could just decide on a wheel....