just starting out in Unity.

I tried to include a tile asset into an isometric tile palette. However, I can’t manage to make its size match exactly one tile of the grid all while perfectly covering it. On paper it works without aligning with the grid but this announces hell for later.

Grid Cell Size: 1 / 0.5 / 1
Palette Cell Size: 1 / 0.5 / 1
Image Size of the asset: 128 x 128
Pixels Per Unit: 128

With PPU 128: the asset seems too large and is shown below the grid.
With PPU 256: places the asset precisely onto the grid as wished but is 4 times too small

What would be the necessary setting that I overlooked or messed up?

With PPU: 128 https://i.sstatic.net/e8tMn6vI.png
With PPU: 256 https://i.sstatic.net/824BnZnT.png