I'm not sure I've seen such a reference myself. It's just rules of thumb that get passed down in practice. In such a case (like you've got here) you would reinforce the perimeter (select a effective width, maybe 12-16") and reinforce it like a (stand-alone) wall. Between that "wall", is just considered fill. The re-bar you have going each way in the orthogonal direction (in the "fill") is a good idea too. (For crack control. Obviously, if this is some sort of environmental structure, you would need a detailed analysis for that.....and could no longer consider it "fill".)
Your perimeter would have to get as wide as necessary to insure that any anchor bolts fall into a reinforced zone. (Even if that means adding a "wall" in the interior to pick up any anchor bolts or support skids.)
