That fixed it, i don't see the gap on the right anymore.
As for the default window position, i'd say center screen is probably best for an interactive window. You could add another set of <> buttons to toggle between the default window positions if you want the user to have a choice.
As for the pixel gap in the bottom right when defaulting, i prefer it having that gap vs not. While 0px would be more factorio-like, i dont mind the 12 px gap. It has the added benefit of not clipping on the remote view border as much which appears to be a 15px border.