Distance to Capital

[Kugutsu]

Im pretty sure its hardcoded, so you cant nerf it. If you know what you are doing, you can increase the happiness bonus given to you by buildings to minimise the effect.
Or let them revolt, and when you recapture them, slaughter the inhabitants. That'll teach them to be revolting, and it will keep them quiet until they breed back up to capacity again...

[MarcusAureliusAntoninus]

Im pretty sure its hardcoded...

And there it is...

...If you know what you are doing, you can increase the happiness bonus given to you by buildings to minimise the effect.

I usually double the garrison happiness and add law to educational buildings.

[Kugutsu]

Personally I think distance to capital is no bad thing. In those days, if a province was 500 miles or more from the capital, its only natural that it would only feel loosely affiliated.
Far more annoying for me is squalour. Rather than reaching a point where it negatively affects order, it should instead create massive growth penalties, so the population effectively stops growing. But I have said this before in another thread...