Mass gatherings

Sometimes on the campaign map, that in a siege or defense, both groups keep gathering more and more reinforments along side the besieged city, It's just like the cold war, with the nuclear weapons, the enemy gets some more soldiers then i do this to. And this is can pretty much go on for ages with no fighting at all, but when the fighting starts its all hell breaks lose.

I have had this several times, the worst case was against the timurids when i had gathered like 4000 soldiers to defend a single city. More recently i had this in the Britannic campaign but i managed to destroy the main army's at night on by one with Wallace. Actually i find these kind of conflicts the most fun because, in battles like those the outcome of wars are decided wich makes the battles all the more exiting because there is much to lose, and much to gain

Anyway does anyone else ever allow this kind of stuff to happen or do you guys attack before hand?

I generally will not let it get that far along. I bring mass numbers to bear as quick as possible.