Spacing between elements in Horizontal Layout or Grid Layout

I'm trying to get images within a Horizontal Layout (or Grid Layout) to appear closer together. I have spacing set to 0 and I've tried adding left and right padding, but I can't find a way to make this simple adjustment. The alignment is fine, I just want less space between them. When I add padding it doesn't squash them together as I'd expect, the layout just overruns the container (or in grid layout, the images wrap).

I'm scaling the images to get them the right size, is this affecting the spacing? I mean is the spacing being determined by the original size? Any help would be appreciated.