You said:

:A self-bailing SOT configuration
: means the seat has to be above the draft of the hull..right? If the draft
: is 3", the seat needs to be 3"+?

I don't know about the ratio you're thinking of, but I've seen self bailers that can draw down the water to something slightly below static by the venturi action of the bailer, i.e., when the boat is moving, venturi action sucks the water out of the cockpit to a level below water level. Of course, when the boat is sitting still, the water will pond in the footwell (or seat) up to the static level. Surfskis commonly have self bailers in the footwells but the seat is slightly higher and molded so closely to your butt that there's no room for any significant water to accumulate so there's no provisions for a self bailer. SOT's usualy have the feet below the butt sufficiently to reduce or eliminate the need for a backrest. I find those SOT backrest contraptions worthless anyway, so if I were designing one, I'd get my feet down low enough to do without the backrest. My one-man outrigger has about 8" drop from the seat to the bottom of the foowtwells and is very comfortable without a backrest. Of course the ama handles all of the resulting instability.

Sorry to stray so far off-topic, just had my morning cup-o-joe!