Money, money, money! The Dinwiddie @ Hopewell game drew a huge vistors gate. Plus the local rivalry factor. The central district is composed of 3 3a's, 1 4a, 3 5'a's and 1 6a. This is how things would look under your proposed plan.
3a. Hopewell, Colonial Heights, Petersburg, John Marshall, George Wythe, TJ and John Marshall (same as you have).
4a. Powhatan, Midlothian, Monacan, Dinwiddie, Huguenot
5a. Matoaca, Prince George, LC Bird, Meadowbrook,
6a. Clover Hill, Cosby, Manchester, Thomas Dale, James River
As you can see there are not enough southside teams to make an entire district by level for the higher level teams. Who would they play and stay within their travel budget. If 3's playing up is bad for you why would it be okay for the other divisions to play up. Also you would likely have to play someone twice (playoffs) and no one wants to do that in the early rounds.