Having a look at the tiles, I even could try to create two other tiles being ground tiles, but without having a “shining through” border above. So we even could have four new tiles:
Two to create a more even floor and two to stack higher.
If you also want these two additional tiles without a “shining through” border above, please also mark in the “copy” tileset where to place them on the modified tileset.
Do you want me to add the missing tiles?