Current border width available in the UI via options slider is limited to:
floor(min(bar_height, bar_width)/8)
i.e., for every 8 px in height the bar is, you can have 1px border.

The original intent behind this was to attempt to save users from themselves, e.g. make it so they make the whole bar their border and can't see any of the actual bar.

The maximum width the bar should really be (in which case the visible part of the inner part of the bar would be 0) is:
min(bar_height, bar_width)/2

This also doesn't feel right to me, but there should be some middle ground.

Thinking about what this should be but logging it to not forget.

This is now /4 instead of /8