Im not too sure. But I've heard a bit about how the guild econ. works.
From what i've heard you have to keep that castle for as many WoE's as possible.
Something like in trying to rank your Slim Pot Maker.
Hold a castle for 1 week (2 WoEs) you get 2 Points
Hold a castle for 1 week without loosing it ever (2 WoE;s) 4 points
and so on.