Relative positioning doesn't play nicely with --scale
xrandr --output FOO --scale 2x2 --above BAR (and --left-of, --right-of, etc) appears to use the unscaled display height and width when determining the position to use.
It appears that
--scale affects the transform information for the display but does not change the mode; but
--above and friends look at the mode but do not check the transform info. Based on briefly checking
set_positions I think the relative positions are the only places that calculate a position this way; I think a patch would be easy (but I don't think I have time to send one).
The result is that in the given example output FOO is only offset by half what it should be, and overlaps the top half of BAR.
This configuration is motivated by a combination of high-DPI 4k laptop with casual-tier 1080p monitors.