Using version 3.8 (didnt see any patch notes about changing/fixing this since then)
With the old UI Sprite, using Unity Atlases, the "pixel size" is factored in when doing Snap/MakePixelPerfect. If set to 0.5, the sprite size will be half of the raster's size.
With the new UI2D Sprite, the pixel size seems to have no impact on Snap/MakePixelPerfect. Am I missing something?