Thanks all for the comments. I'm still trying to learn how to use the darn flash. Struggling between getting the right amount of ambient, and not making the flash so obvious.
The flash actually fired on the 1.8 shot in HSS mode, but no return was detected, and I wasn't sure the TT685 could provide enough light for that shutter.
I've got one from another location where I think I got it better, and because of the shade, I was able to keep the shutter speed to 1/250th and aperture was f/2.5... No f/8 to compare with, though...
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I actually had both the TT350 and TT685 with me. There was one location where I tried to set up a shot with one flash being the master but not firing, and the other would fire off camera. But I didn't remember all the settings I had to change and couldn't get the off camera flash to fire. And I left the manuals at home.