It’s really interesting and kinda cool (although it can get frustrating) how often different fandoms develop different standardized porn tropes. There are fandoms that follow the old 1-2-3 fingers and then cock rule, and fandoms where that sequence is Verboten, fandoms where two guys always take a mental moment to see who’s bigger and fandoms where size is never mentioned, fandoms where near-simultaneous orgasm is standard fare and fandoms where it’s exceptional… it can be really fun to observe as long as you’re not getting frustrated by a lack of variety within a given fandom.
Hmm... I wouldn't have guessed that this would be strongly correlated with particular fandoms. Do you think there's some seed-effect at work here, where early works in a given fandom are really really influential, and then people who are into that trope/structure are attracted to that fandom, and those who aren't are repelled?
The same way that larger things like "Ao3 house style" presumably filter new Ao3 users for being predisposed to like that style.