Doesn't the icon_map3.dds that comes with EQ2Map already contain a grid? At least the one I have in ProfitUI does and it is based on an old official one, so it's probably correct.
The image file uses 42x42 for the icons including the 1px border, leaving a net space of 40x40 for the actual icon. Whether the XML references that correctly I don't know since I don't have it at hand.
