I've resorted to running a shell script every time I plug in.

displayplacer "id:... res:2048x1330 hz:120 color_depth:8 enabled:true scaling:off origin:(0,0) degree:0" "id:... res:3840x2160 hz:30 color_depth:8 enabled:true scaling:off origin:(-918,-2160) degree:0"

displayplacer is very easy to set up and also gives you access to modes that you can't access with System Preferences.