I think you may need this plate. (but best to call Vortex customer support to confirm this plate w/ Defender will fit your XDM Elite firearm):
Springfield Armory WebStore
store.springfield-armory.com
According to this article on the Vortex Defender, it's base on the Shield RMS footprint.
Vortex Optics has just released the Defender CCW micro red dot sight, designed for concealed carry and sporting an interesting new feature.
gundigest.com
Part excerpt from Article above:
"The Defender CCW is available with two reticle options—either 3-MOA or 6-MOA—and it mounts via the common Shield RMS footprint. The optic is small enough to be used with micro-compact handguns (as well as full-size pistols), but Vortex claims that it features “the biggest sight window in its class” to help users shoot with both eyes open and maintain superior peripheral vision and spatial awareness. The unit is 1.6 inches long, has a weight of only 0.95 ounces and was designed to have a slim profile for a snag-free draw."