Before I first got my 595s, I read a review that said they were actually more comfortable than the 650s. Unfortunately, I found out they were right when I got my 650s. I would wear the 595s for hours on end and not feel my head overly squeezed or weighted, or my ear suffocated. This was not entirely my experience with the 650s.
After making your suggested adjustment, the 650s were significantly more comfortable to wear.
However, tthey are still not as comfortable as the 595s. At first I thought this was due to the 650s outweighing the 595s, but Sennheiser lists the 650s ten grams south of the 595s. Perhaps it is because of their plastic, more flimsy build, but even to my hand the 595s weigh more. If there is really only a ten gram difference (260 vs. 270g), my assumptive (placebo) stance could easily outweigh the real difference. It seems to me that both cans share a very similar range of motion adjusting to the head, so I'm curious why the 650s still feel less comfortable, even after they're just as 'loose' as the 595s.
Does this mean I'll be spending anymore time with 595s than the 650s? No. It does, however, mean I will be spending less straight hours with the 650s on my head as their pressure builds noticeably for me.
1time: Thank you very much for taking your time in making this post. The adjustment didn't make my 650s the most comfortable set of cans I've ever worn, but it really, really helped. I would definitely recommend doing it for anyone who think that their 650s might in any way be too tight. Thanks much!