I'm trying to work up a kinkmeme fill from the POV of Character A, who is anally fisting Character B, on B's specific request. A and B are in an established relationship that has previously involved other forms of anal play, and A is quite sexually experienced and an open-minded "try anything once" type, but he has never done this specific act before. A's initially somewhat reluctant, but gets more enthusiastic as the scene goes along and he sees just how much B is into it and how much trust and vulnerability is involved, etc.
Setting, I'd rather not give away the specifics, but it's one that plausibly has full access to modern commercial lubricants, sex manuals, print and video pornography, and so forth; there's no reason for A and B not to have access to the supplies and information that will help them play safely. I've already read Jack Morin and Tristan Taormino and sundry other sexperts, watched lots of video clips and read through postings on Fistforum.com -- I'm fairly confident that I'm good to go in terms of the general mechanics and mindset of it all, but what's stumping me is finding much in the way of detailed descriptions of what sort of *physical* sensations the penetrative partner is going to be feeling in his hand/wrist in terms of heat, pressure, muscle contractions, etc. I've Googled on a wide variety of search strings involving "fisting"/"anal fisting" + various permutations of "personal stories", "first person experiences", etc. and unsurprisingly most of the results were porny first-person fiction or how-to articles; most of the non-porny personal accounts tend to be written from the POV of the fistee, and that's just not helpful to me here; while A has been around the block quite a few times, this is something completely new to him and I want to try to convey that sense of discovery. Any personal experiences you can offer for the sorts of things he is likely to notice and focus on here are deeply, deeply appreciated -- anon responses are quite welcome!
(OP does at least have experience anally penetrating partners with fingers/toys, and has also vaginally fisted women -- if anyone is able to make specific comparisons of vaginal vs. anal fisting from the top's POV, that would be especially helpful.)