What you have set up is no different than having the Flex directly on the camera hot shoe, so it should work just fine. I assume you are trying to achieve is a little faster SS using the PW hypersync feature. What firmware version are you using in the Flex? What camera body are you using?
I have played with the hypersync feature in iTTL and could not gain any benefit over the 1/320 SS factory default when leaving the flash in iTTL. It is my belief the flash needs to firing at 100% before you will see any gains. In other words, the feature is using the light tail from the 100% pop. In iTTL, the IGBT might shutdown the flash if full power is not needed.
I'm using a D700 and have the latest PW firmware installed, and that, as I understand it, automatically sets the timing for Hypersync operation.
Yup, still rasslin' with night football and I'd love to get 1/400 or 1/500 with full flash, like I can with my D70s I've never been able to get the "2 stops under ambient" recipe to work in a manner where I like the images.
Thanks for sharing your experience - no better than plain ol' AutoFP at 1/320, eh?
I wonder if setting the flash on MASTER might yield different results?
I see you put this in two places. According to the PW wiki you will still need a transmitting radio in the camera hot shoe. There was some talk about PW making changes that would allow a single radio to do the hypersync, but I didn't see that in the ver 3 release notes, but I will try it today. If that's true, your setup should work. I just don't believe it will work well in iTTL. You need the light tail of a full power pop to see the benefit.
If you set the flash to Master, the PW radios will not work correctly.
On my 5d, I couldn't get more than 1/250. With 1/320 I would get some small black bar. On my 1dmk2, I could do clean 1/500 with some very small bar at 1/640. This is with Hypersnync alone.
On another note, the D70s has an electronic shutter because of its CCD sensor. You can easily shoot past 1/500th shutter with flashes, so long as the camera doesn't recognize the flash. I just used regular pocket wizards, and easily shot at 1/1000th on a D40 (similar CCD sensor). After further tests, I was able to get 1/1250th consistently, and 1/1600th with a few blackouts.
I've never been able to get the "2 stops under ambient" recipe to work in a manner where I like the images.