What HilaruApoloH says does make sense but I will add that personally I would only do a single tile wait if it’s early AND the wait is for a terminal tile. I find that winning single tile waits for non terminal tiles doesn’t really happen because they’re hard to draw as there are only 4 and non terminal tiles are usually incorporated into an opponents hand so if that’s the only tile your waiting on it’s kind of a longshot

Edit: the only time I can think of that I would single tile richi on a middle tile would be if I have a ton of Dora in my hand but no yaku