The best answer I can come up with is the result of testing several outboards
on a flat bottom plywood skiff over the past three years. I think I just like test rides.
Without adjustable trim tabs on your transom, this will produce the best results...
Make an inclinometer, a simple tool for measuring angle from vertical.
Simple to assemble from easily obtained components (sinker, fishing line, protractor)
Using a carpenters level, set your hull so the keel is horizontal.
Then install the inclinometer on the hull so it reads 90 degrees. (vertical)
After installing the inclinometer, raise the bow until the inclinometer reads 85 degrees (5 degrees from horizontal)
With the hull inclined bow up to 5 degrees from horizontal, adjust the trim setting
of the outboard so that the anti-ventilation plate is horizontal using the carpenters level.
The result looks like this...
Now adjust the outboard, using the clamps and shims, to raise the outboard
until the anti-ventilation plate is level with the bottom of the transom.
This height setting will work for most factory propellers and looks like this
With a cupped propeller it's possible to raise the outboard higher
until the top of the water inlet is just below the level of the transom
looking like this...
Without power trim tabs to reshape the flow of water, that is about as high as you can get.
doesn't matter if the engine is transom mounted or on an 8 inch setback.
Water flow out from under the hull at planing speeds stays almost level for about 2 feet
and the water inlet has to be below the surface of the water.