Your answer makes a ton of sense, it really does. But once you get 2 generals pin defence, each with a retinue, don't you think they become fairly powerful buildings? I mean you have2generals, their retinue, and the castle itself to contend with. Shouldn't there be a strategic way to take it out of the equation?
Because if you increase the radius, you are inviting a host of attacking issues and guaranteeing certain things will no longer be able to occur.
In not saying that this is totally a bad thing, but I question whether or not the answer is to make it so that other ages cannot attack a higher one because you've made the castle a impenetrable fortress for anyone under that age.
In the era of sandbagging, giving that sort of I've sided advantage, increases the likelihood of Sandbagging growing, because now not only will I be paired with ages way below me, but now I have a building that they simply cannot contend with.
Does that make sense?