Thanks for the question. This issues is caused because of the way in which the A2S array calculates rows. It's best of think of an A2S array as a stack of independent L1S Arrays. The segments in any single row can be of variable widths and the array will adjust automatically, however individual rows are not aware of the segments above and below them and cannot automatically adjust to overlap one another. The height of any row is therefore determined by the largest segment used in that row, and if the heights vary, as in this example, you'll end up with a gap.
Luckily the example you are creating has got rows of slabs with a fixed height, you just need to turn the array on its side like so:
As the green lines indicate, in this configuration the slabs in each row have the same height so no gaps should appear.
I hope that helps out, if you need further help please let me know and if you're able to attach your file I'd be happy to take a look at it.