Help diagnosing 7x17 light leaks (not a newbie, but still)

[G Benaim]

So, I finally got my 717 going and just developed some negs, and about half had some sort of light leak. The holders are s&s and the camera is a folger and schwing w a back tailor made by Ritter to match these holders. In the more severe leaks the back was uncovered but in shade, on the others the back was covered by the dark cloth but in full sun. All the leaks occur on the flap side fwiw. I'm guessing it's my technique when pulling the ds, though I made it a point to hold the back down as well as keep it covered, so not sure what's going on.