I tried playing with the padding ratios in the layout.nut file, but I was unable to create something like I made in this photoshop mockup.
I see what's the point here: Arcadeflow is built for flexibility so in order to accomodate different aspect ratios for games screens or box art, each "tile" has a square area that can be used to draw the actual screenshot/box-art. Depending on the aspect ratio, which is limited to a range from 1:2 to 2:1 (wider aspects are cropped) the actual "corners" of the artwork follow a squircle curve, so when different aspects are mixed together on screen, they all look with a similar area. This means though that very "tall" aspects, like 9:16 in your case, will have a large padding on the left and right and at the moment this can't be fixed because the tile real estate is, as I said, square.
I can see if changing the aspect ratio of the tile might mitigate the issue, but that's a deep change and will probably take some time, unless I do some dirty trick like altering the tile spacing. So let me think a bit about it and I'll get back with a solution (hopefully

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