Gridly's home page is a grid of boxes of the most recent posts. The maximum width seems to be three boxes across, matching the three footer widgets. With smaller device widths these numbers are reduced.
The problem I see is on my iPad (landscape) where I have only two boxes across, even though there is room for three. This is evidenced by the fact that all three footer widgets are side-by-side.
Of course there's no developer support for this free theme, but I'd sure love a tweak that would allow three boxes across on all devices that have room.