OK... I still did not get to the pool (and I might get some time in tomorrow), but I did get some time in with better testing in the tub! (just and old fiberglass bathtub).
Here is what I did...
> Used an Inon D2000 strobe as my "subject" since it had several qualities that I thought would help me decide on focus clarity.
> Used 2x BigBlue 2500 lumen LED torches as my ambient lighting (which afforded me an ISO of 400 and shutter of 1/100 - 1/125 at various apertures)
> Snipped several bit of old measuring tape (the type that is stiff and rolls into the case by itself) so I could measure distance, but also because the fine lines and graduations would give me a better objective to judge focus.
> Tested distance of 2", 4", 6", 8", 10", 12", 18", 24" (inches) all at f11 (I've been able to prove to myself that this seems to be the aperture sweet spot), but different focus settings (0.3ft, 0.4ft, 0.5ft, 0.65ft, 0.8ft)
> I wanted to test 2" and 4" shots, but I'm weighting them quite low as I do not intend to shoot 4" and in. Still, I took them as a reference to help me figure out what was going on
> As a final test, I used several objects set in background and foreground and tried f16 and f22 at the 0.65ft focus, as well as f11 (again) and f8.
Here is what I found...
* 0.3ft (minimum focus) and 0.4ft were all pretty much rubbish except at the 2" and 4" distances (actually, even the 4" distance was rubbish with the 0.3ft focus)
* 0.8ft looked best only beyond 6"
* The 2 contenders for best DOF seemed to fall to the 0.5ft and 0.65ft shots.
* As one might suspect, the background focus was slightly better at the 0.65ft shots, while the foreground focus was decidedly better with the 0.5ft shots
* f11 was a clear winner in the final test shots (I think this is the sweet spot of the lens overall)
* @ f11 and 4" - 6" - 8" - 10", 0.5ft & 0.65ft were virtually identical - I could not call a winner
* @f11 and 12" (and beyond) 0.65ft was more clearly the "winner" as the distances became longer.
So now I considered f11 focused at 0.65ft (which was actually as close to exactly between 0.5ft and 0.8ft as I could guesstimate) to be my decided "winner"
Now I wanted to "see" what f22, f16, an f8.0 would produce... and f11 was the clear winner.
Conclusion: In my limited testing, I would choose f11 focused at as close to exactly between 0.5ft and 0.8ft on the focus ring as my correct hyperfocal setting for anything 4" and beyond (excepting 2" and 24"+ - in which case I'd choose 0.5ft for the 2" shot, and 0.8ft for the 24"+ shot)
ISO 400 1/100th f11 (2" with focus set to 0.5ft)
ISO 400 1/100th f11 (6" with focus set to 0.65ft)
ISO 400 1/100th f11 (12" with focus set to 0.65ft)
ISO 400 1/100th f11 composite
PS - I do get the tinyest mechanical vignetting with this Dome/lens combination (again - Athena 100mm fisheye dome for Oly PT-EPxx [designed fromLumix 8mm] with a Rokinon 7.5mm fisheye)