I would think the percentage method would work fairly well. If you were to take the basically straight portion of the deck, reduce the height by X% and bend a thin strip of wood so that it is horizontal at the center line and tangentially hits the deck over where the straight part starts, you should get a fair deck. Check it before you start strips and make any last minute adjustments needed.

> Your deck looks pretty good. I tried a similar approach on a
> few of the center forms, but didn't like the results. I'll next try
> reducing the peak of the deck some small percentage of the height
> of the deck from the sheer and running the curve through that point.
>