I really like OP's idea, and i think that there really shouldnt be a cap on how high LA could get, instead you would have a system of monthly LA change that depends on a number of factors like, tech, tech group, government type, ideas, and policies and it all ties in to distance from capital.
So Russia at say DIP tech 12 would have a x monthly LA change for provinces at y distance, this way at low tech levels it would be harder to control a vast empire but it gets easier with better technology, up to certain point.
Good idea, although I wouldn't want to make the system too complicated. I like the tech idea though, as governments historically got more efficient as the modern ages progressed. Perhaps just an occasional -0.0x as admin tech progresses.
Oh and @Pilon I will try that thank you. I'm also going to make a post in the Suggestions forum for the devs.