What sounds like a tongue twister is more of an irritating detail I noticed just now. In the grand scheme of things, it is absolutely meaningless. Unfortunately, the meaninglessness makes it even more irritating… Ugh!
So, to get it out of my system, let me show you the depth gadgets of Kickstart 1.x on the Amiga, used to send screens and windows to the back and to the front, respectively:

Did you see it? The right gadget is wider that the left gadget!

Irritating, right? I guess with the separating background-colored vertical bars being part of the gadgets, the middle bar had to be included in either of the gadgets. Kind of like an airplane armrest situation!
This specific solution is sensible, though: The right, wider gadget is the foreground gadget, and bringing things to front surely is more important than stuffing things away! Speaking of which, I kind of feel better already and can happily stuff this little nuisance away. Thanks for reading! :)
PS: Must… resist… urge… to compile a complete screenshot and width table for all OS versions in Topaz 8 and Topaz 9 mode