I was trying to create an atlas using atlas maker in substance designer but I have an issue with the masking sizes.

Maybe I don't understand how that works but I thought I was supposed to get a mask that would be 256 pixels offset to the right and with a size of 256x256. What happens though is when I open the uv snapshot in photoshop, the sizes don't match, this is what i get:

What am I doing wrong here?
Thanks
Replies