Update! (tiles added)
I've updated the tileset with a new autotiler (located on GK_FV_A2.png) for RPG Maker MV/MZ that you can use to create cliff tops. Due to this I was able to remove some tiles from 'GK_FV_A5.png' to improve readability of the tilemap. I've also added 3 new tiles to 'GK_FV_A5.png' for the bottom left and right side of a straight cliff side, as well as one more sand variation.
For non-RPGMaker users, the 'MainTileMap.png' has also been updated to match the above. The tiles for modular custom cliff top are located on the far right of the tilemap now.
I hope this helps!