If the ground plane pair is large (covers most of the board), it doesn't much matter where you place the caps, as long as the connecting traces and vias are short (you can shorten these further by using two trace+via per pad per capacitor).
There should be a reasonably sized bulk cap also attached to the plane, of capacitance several times the total bypass capacitance value, and ESR suitable for dampening that network (which for a plane with tens of bypasses attached, will probably be in the fractional ohm range, where tantalum and aluminum polymer are most desirable, or ceramic probably with some added ESR).
Tim