You have to understand how optical ttl is working to understand why these modes don't work.
I have an Inon D2000 so I'll talk from that perspective, but it's the same in entire inon line and I think sea&sea also.
In inon sttl mode, the strobe is basically watching the camera flash and quelching it's flash at the same time. So, the camera has to be in a mode where it's determing flash duration. Otherwise the external strobe has no timing signal to work off of. If you put the camera in manual flash, which is what you're doing when you select 1/64, then your strobe sees a flash that has nothing to with the exposure for that picture. It's seeing whatever you told the camera strobe to do.
So, if you put the camera in manual flash, your strobe becomes manual.
Now, on an Inon, the way to try and work around this is to use the external auto mode. In this mode, the inon strobe is determining flash duration itself with no input from the camera other than when to start. If using EA mode, then put the camera on 1/64 to save power and quicken refresh time. At this point, you're constricted by the recharge of the inon strobe itself and not the camera. But, from experience, I can tell you that EA is not as consistent in getting the exposure correct as using the cameras ttl with the strobe in sttl.
On my epl2, I'm generally in manual with flash set to fill and my D2000 on sttl.
I find the D2000's recycle time is similar to the epl2 being ready to go again.
Of course, you can always go full manual with camera and strobe as you've already figured out.
Edited by chris_l, 18 July 2013 - 11:58 AM.