Just dreaming here... But if there was a "target province" and next to it, "target holding" thing, pr. action, then it could show local prosperity, size of province, and on the "target holding" you would be able to see level and owner of all holdings in that province.
Using those values, combined with the action type, would then fill out the formula on its own.
On your Domain page, in the DO, you'd specify which is your own domain and what other domains you have "holding advantage" deals with.
Of course, then we are almost building a game engine... :-)
Some elements could probably be driven by volunteer work.