I printed out the ACE Pro Dual Stack from Another3Dprinter. Love it Love it Love it. But each time I went to push the lower try in it wouldn't attach to the magnets. After playing with it for a little while I found if it was exactly centered it had no issue. So when it was seated correctly I measured the space between the rack and the tray. I made this quick tray guide that just drops in and takes up the extra space and keeps the tray centered.

Print two. One for each side.