I guess from time to time everybody runs into this frustration. I see that the computing-intensity is a problem, but cant it be precalculated once?
The "hit-ability" of a given coordinate on a map is just a function of a given PD and its Placement-coordinate. Both are constant through the game so its possible to calculate a table pregame and read it. That table could as Property of the map. To minimize this, you can spread the coordinate a bit - we dont need pixel-accuration here.