If the game says you need 10 for full coverage, then you need 10. If you don't need 10, then why is the game saying you do?
That is, at least, the impression the game gives you. And this is reinforced by the messages it gives you every day: " Too few estates support production and tax collection. Too few estates exert authority and support the local police. Lack of knights reduces region control." i.e.: "You need more knights."
If 80% was enough, why are we telling them they don't have enough?
I suspect that most of this will be worked out in the estates revamp.
