Each layer is only a max of 4 images:

There is one image per transparent corner.  0.png has no transparent corners, 1.png has 1 transparent corner, etc.  

here's another screenshot with the LPC assets

Updated to have different tiles for bottom edges and top edges to give a slight perspective like many tilesets are made to be.

Though it requires 3 more tiles of course.  Here is what each layer looks like (4x2, with the two left most being two variations of fill patterns)