Unfortunately Start11 requires a resolution that is 1200 pixels wide to use the config screen. 1200 pixels wide at 125% scaling is only the same as 960 pixels and at 150% it would be 800 pixels.
I appreciate this is annoying, but as I am sure you can imagine such low resolution portrait modes are extremely uncommon usage especially as a primary display. If you used a tablet I would say just rotate it to use the config screen but I understand you are on a desktop PC so that wouldn't be as easy.
If you use 100% scaling you should be ok though or you can move the window left and right as you need via the titlebar. Not ideal I know