get the right Derailleur.
too far to go with a funky b screw adjustment.
the problem is that the jocky wheel touches the 28 tooth cog.
Bah. It's only one tooth more than the rated capacity. I've been running 11-28s with DA7800 RDs on multiple bikes for several years now with no problems.
There probably aren't that many bikes out there that it won't work fine on.