The wiki article is probably out of date. In Dec 2020 (r5663), grid drawing was changed to support screen sizes other than 360x240. This change would be in 1.6 and later, not in 1.5. The commit comment says "Support for cameras that do not have 360x240 bitmap screens. Grid is scaled and centred on the screen with grid aspect ratio kept at 4:3."
G1 X is probably not 360x240, but I'm not sure offhand what it is. Note the original cams were 360x240, but still 4:3 aspect ratio, meaning non-square pixels.
I'd suggest trying something simple, like a 360x240 box divided in quarters, and see how it shows up.
There should be a thread where this change was discussed in more detail, but it wasn't linked in the commit and I didn't find it in a quick search.