Start with:

Hidden Mafia - Hidden Town
Hidden Mafia - Hidden Town

Hidden Any - Hidden Town
Hidden Any - Hidden Town
Hidden Any - Hidden Town

Hidden Town - Hidden Town
Hidden Town - Hidden Town
Hidden Town - Hidden Town

Hidden Town - Hidden Any
Hidden Town - Hidden Any
Hidden Town - Hidden Any

Hidden Town - Hidden Mafia
Hidden Town - Hidden Mafia

Now assume 1 - 2 hidden anys are mafia/neutral in each.

Hidden Mafia - Hidden Town
Hidden Mafia - Hidden Town
scum Hidden Any - Hidden Town

Hidden Any - Hidden Town
Hidden Any - Hidden Town

Hidden Town - Hidden Town
Hidden Town - Hidden Town
Hidden Town - Hidden Town

Hidden Town - Hidden Any
Hidden Town - Hidden Any


Hidden Town - scum Hidden Any
Hidden Town - Hidden Mafia
Hidden Town - Hidden Mafia

We're already at near 50/50 with it being 6s vs 7t with only 1 hidden any being scum... now I know you'll say what if mafia is neutral in the other making it s/s. Well, my math showed only 1 hidden any being scum - I can easily increase that to balance it out. 13 player game standard is 4 non town so even with some overlap, Town/town players most likely are not the majority today.