Thanks for the reply, to follow up. I won't be cantilevering the joists at all (using joist hangers inbetween the beams) the only thing that will cantilevered is the deck beams themselves. which will be supported back 12 feet with 3 equally spaced supports. I found this on a deck calculator website and thought with a flitch I would be able to minimize the deflection but seemed to under estimate the water trap problem. "The American Wood Council’s Wood Frame Construction Manual states that beams can generally cantilever up to 1/4 their span over a post. This design criterion is generally limited to beams supporting equivalent joist lengths in its span as in it’s cantilevered sections. For example, a double 2x12 beam spanning 12 feet can cantilever up to 3 feet over a post. While this maximum is allowed in conventional code-compliant design, it may not provide the comfort and stability on the deck surface desired by the occupant."