Expert level! How do I resize a selection, like tolerance, so my selection gets exactly the same pixels from the edge of my figure?

How do I resize a selection, like tolerance, so my selection gets exactly the same pixels from the edge of my figure?

If I resize the High and width, dosen't the space between the selection and the edge of the figure get the same size.

I know it is possible, because I once saw it on a video, but I didn't thought I would need it.

Thanks for the help!!