The Dominion allows only the top 4 teams to advance to the district tourney.
Cosby has mathematically clinched a tie for first, and will surely win at least one of its last three games to clinch first outright. (They also have tie-breakers on James River and I think on Manchester also, so it may already be official.) Under what I understand is the new regional format, Cosby will play the # 2 team from the Capital in the regional quarterfinal round.
James River and Manchester are tied for 2nd. Manchester beat JR head-to-head in their first meeting, but in all likelihood the tie will be broken by their rematch at JRHS next Thursday. Both teams have clinched playoff spots, but they surely hope to stay in 2nd and 3rd so as to avoid having to face Cosby in the playoffs' first round.
L.C. Bird is currently in 4th but only 1 game ahead of Clover Hill, so that is still in play.
If the season ended today, the playoff matchups would be Cosby v. Bird and Manchester v. James River. If Cosby were to beat Bird, the Manchester-JR winner would also advance to regionals irrespective of the outcome of the district championship game. In the event of an upset by Bird, the tourney championship game would determine the district's second regional representative, who would play the Capital's # 1. (My understanding is that Hanover has that pretty much locked up, but someone can correct me on that if I'm wrong.)