Slick mode (or it?s respective User Mode setting) is the only mode which deactivated ABS at the rear.
The other modes Rain, Sport and Race alter how sensitive the ABS is, all are linked though to what percentages I don?t know.
In these modes, pulling the front brake lever partially activates the rear brake. However, if you only use the rear break the front brake does not activate
I personally like the ABS setting in Race, unless it?s Winter in which case I change to Sport