This is likely an oversimplification, but I thought the game plan for Fitz was established 5-6 years ago: sit on everything short, stack the box, give him man coverage on the outside and dare him to beat you over the top.
That's what I recall from his time in Buffalo. Once opponents keyed in on FJ and sat on the quick stuff our offense stalled. He doesn't have the arm talent to make you pay on the deep ball. He throws them 5 feet out of bounds or underthrows resulting in INTs.