@epicgamer23 The order of the things around the x can be used to say who's in charge, taking the lead and that sort of thing. For instance, if someone called something an Uzaki x Sakurai doujin, she's basically having her way with him. Flip that, and maybe it's one about him finally giving into his lust and basically attacking her.
So, in that regard onee x shota, an older female is taking the lead with the young boy. But flip those positions, and now some uh "precocious" child is taking advantage of the older woman, perhaps she's coming off as weak willed and he's bullying her into things? That's the kind of stuff you can denote with just the order you place them. This practice pretty much arose from Yaoi, where the fans considered the order of character names to be worth friggin' blood feuds, 'cause it was saying who was the top and who's the bottom.