I know its quite a bad drawing but the way I see it is the first drawing is a "normal" head, never been skimmed, with red area being the squish area.

Second drawing, head been skimmed and the white bit is the part of the squish that has been "lost" in the skim. Am I right there?

Third is with a decomp. plate added (red). As the plate is around the valve area only and does not replace the squish that is missing(white area), the head has just been raised... still ok?

Fourth is I guess the sort of plate that would be needed to get the squish back to normal....

Am I almost right or shall I get back to my kitchen???