confused with importing pixel art sprite and it's PPU settings

Hi I'm new to Unity.

When I trying to import my 32 x 32 pixels sprite (made via Aseprite), I got a problem.

Each sprite in my importing sprite sheet is 32 x 32 pixels, So I expect to see them locate in 4 grids in my Unity scene, like I see in Aseprite editor (below).

But when I set the import setting's PPU to 16, my sprite seems too small.

I need to set PPU to 8 to meet my expectation.

Why is that?

Do I misunderstand something?

Thanks!

BTW,

1)My reference is this tutorial
https://www.youtube.com/watch?v=E9GilOgdW2M

2) My world grid setting is 1 for XYZ.

Thanks Again!