@Kwarcdymny1 I did my own version/demo of the things you showed in your video (which was clear and well done!) and I also went in at a ground level angle at some points so that you could see more why certain times where you want to add tile next to the pool don't work.
Adding tile right to the edge of the pool requires that the ground there be completely flat already, which it was not at times. The reason the tile went right next to the pool in the two cases you used was...
1. ) Where the terrain height tool was not used at all (on a flat lot), or
2.) Where the tile is placed first (which forces the area the tile is placed on to flatten, then the pool is added within the flat area of the tile.
I also hope there will be changes to make some of this more user friendly. https://youtu.be/UzDHcTKTcOM
@Kwarcdymny1 - I have 2 work arounds for you, which I use for this exact problem.1) Put your pool in the flat square foundation piece having the foundation piece extended further out on all sides of the pool then the tiles should place no problem. 2) Pull your pool in on all sides, place tiles, pull pool sides back out.
