In addition, even if you strip the copper, be aware that having extra the dielectric of any substrate like FR4 will affect the radiation pattern. As has been suggested, always follow the documentation for this sort of stuff, they will have had these modules in expensive RF anechoic chambers. There will often be recommendations on where to place the antenna WRT the board enclosures too. if not, always have it on the edge of the PCB, and that edge ought to be close to an RF aperture (ie, not in the middle of a conductive case, but at an end with plastic, that's what the black plastic areas are on iPads etc).