Okay, someone on Tumblr found the fic for me and man oh man, I was off by a mile! Some people have a mind like a steel trap. I, apparently, have a mind like a sieve.
1) The fic is 23 chapters long (some pretty short chapters but still twenty three of them)!
2) It’s resolution, which does take up the last nine chapters, is set during the episode “Home.” However, it starts around the episode “Carpenter Street.”
3) It’s on fanfiction.net.
4) I had bookmarked it on ffn because it plays with its inciting “what if” scenario with aplomb, has some serious wrangling of weighty topics and (my weakness) contains a fair amount of humor.
At least it does have a special elderly priest with soulmate sensing powers brought in by Koss’s family, many outsider viewpoints and a very happy ending, so I wasn’t completely off base! >_<;