The reason the ratio is always 1-to-3 is because the villagers actually have a huge advantage in this game - whoever is the mafia-equivalent almost never wins, even in RL games where you can't
secretly collaborate with your fellows, and all 'planning' is done out in the open, during lynching debates.
If you made the numbers more in favor of the civilians (or councilors, in this game), mafia would have even less chance of winning.
That's almost like fixing the game so they will lose.
The same thing goes for the votes. If you don't allow the lynch votes to be changeable (i.e., you can't change your vote), the voting patterns sway dramatically in the favor of the mafia. Yes, innocents can plead their guilt, but so can the mafia - and once they kill off enough people so that they make up half of the population (not all that hard, since theoretically, they could easily manage one innocent during the lynching, as well as their nightly victim), all they'd have to do is vote all together to win. Which would make the game boring, since it would be obvious who the mafia was by then.
When I play this game in RL, sometimes we even do no special roles for the innocents - and the mafia still loses. It just kind of shows you how much harder the game is for them.