I have the XD-M Elite 10mm with the Magwell, and being in MD with its very goofy gun and magazine laws, I had to get all new magazines. Its been long enough that I can't remember for sure, But I seem to remember exactly what Hans Gruber said. I have an aftermarket magwell on my XD-M .45 ACP and I had to shave some of the extended mag baseplate off to get it to fit.
The magazine for the XD-M 10mm for Flush Fit.
The Magazine for the XD-M Elite 10mm with a Magwell, the extended baseplate not only is tapered to fit, it allows an additional round for a total of 16.
I wish Springfield Armory would make the 10mm magwell available for purchase, it fits the .45 ACP. I have called, they do not sell it, even if you asked directly.
Oh, Maryland magazine laws, MD banned the sale and manufacturer of greater than 10 round magazines. But not the possession of them. It is perfectly legal to purchase higher capacity magazines out of state and bring them back with you. So if you purchase a firearm with >10rnd magazine, the FFL has to dispose of the mags or pin/block them before the transfer to comply with the law. And worst, many online retailers that have to keep track of ridiculous laws from 50 states don't know all the details, nor are they willing to risk their licenses on small details. I have had more than one online purchase of a firearm cancelled because the firearm came with >10rnd magazines. Many retailers won't get involved in the intricacies of the law, but its perfectly legally to buy a firearm with >10rnd magazines in the package and have it shipped to an FFL in MD. Under the law its the FFL's responsibility to bring it into compliance before completing the transfer. Either dispose of the magazines or pin/block them.