The scale in Scale display option should allow for values below 1. Without it, we are only able to work around with the xrand option --scale which is not optimal.
This option is to improve rendering on High DPI displays, normal scaling is not the point of it. I suppose I could leave this bug open, but in reality, we're not going to fix this, and therefore I'd like to refer you to other tools, such as xrandr.
Qt does not support scale factors < 1 either.