The MKX has power express up and down for the windows. It's a two position switch for down, hold it slightly down to open the window to the position you want, or push it all the way down for Express down. Same for the UP position.
You need to look at the rear end of a MKX. That is the exact door handle position on both now. And yes, the key fob has a button for just the rear hatch opening that you push 2X's to open or close it, and it's power open and close provided the vehicle is in the Park position.
/Edit: Forgot to add, their is also a button to the lower left of the Instrument cluster for the rear hatch opening, does the same functions. Their is no key opening on the rear. It's all just one button on the underside top of that hand hole.