If you want to open a support ticket, then this is the section to post in. If you just want to ask the community without getting Support involved, then you can post over in Everything Else. 
I think it’s probably because of the optical alignment. Every machine’s ruler would be a little bit different, and also the tray can shift around a little bit (unless you use @timjedwards’ “boots” file – Give that wiggly GF tray the boot!).
There have been some ruler designs posted in the free files area in the past that you can make and attach to your tray. (I’ll let you do the searching for those, though!) 