File Display Border Toolbar Button

I cannot make this work as a button on the border--clicking on it does nothing at all. I have Preferences / File Displays / Border / Set file display to source when border buttons are used turned on.

@ifset:SOURCE=Left
Go DRIVEBUTTONS=fixed,cdrom,network,removable,hideempty,mtp openinleft
@ifset:else
Go DRIVEBUTTONS=fixed,cdrom,network,removable,hideempty,mtp openinright

This on its own should be all you need:

Go DRIVEBUTTONS=fixed,cdrom,network,removable,hideempty,mtp

Buttons on the file display toolbar automatically have affinity to the file display they are over.

Thanks! I had used openin[left-right] for so long I overlooked the obvious.