I have an Ultimate King with drivers backrest on my 2015 B with a Twisted Throttle rack installed. The rack clears the rear slope of the seat by about 1/2" to 3/4". When I install my Givi 46L case there is slight interference with the rear slope of the seat. In other words, the front bottom edge of the case very slightly compresses the rear slope of the seat which then recovers nicely once the case is removed. I used the spacers / risers that were furnished with the rack. Great setup. Only con is that the rack must be removed first if you want to remove the seat from the bike for any reason. Hope this helps.