In that picture, I was getting 371*2 into the AC300's MPPT pair, and 85w into the B300's MPPT directly. Basically, for each B300, you get a 'free' 200w MPPT that most people don't use. How much it helps, I dunno, but I had all but the panels laying around.
What I did was take my 2 3-panel series strings (I had 2 cables coming off my garage), and combined them in parallel to 2 string (still under amperage, voltage stayed the same ~ 95v). Then, when it entered my house, I then split the line and fed it into both solar inputs on my AC300, *
AND* turned on the PV Parallel Enable in the AC300. I assume you need to do this so the system knows not to compete with itself - I really don't know how an MPPT works, and don't really care to learn right now

. It just works.
There appears to be no communication from the B300's MPPT to the AC300 - so I wasn't even sure if it was working until I put that power meter in-line. When we hit sun again, I hope I consistently max out that 200w MPPT with 400w of panels - basically it's a micro overpanel.