To allow for extra politics revolving around coups, perhaps you could also get an extra 2.5% or 5% for every other player in the pool who supports your coup.
I considered this, but given I don't know how many players I would have, I opted out for balance.
The ruleset sounds too simple for a Realpolitick.
It's Risk with coups. It's supposed to be simple, and hopefully be able to run to a conclusion.