Sure, I’m on the road atm but will post a pic when I get back (will be a couple of weeks).
I use to place the o-ring on the flat port, there is actually a small bevel on the outer edge of the glass for the ring to fit. I don’t have the flat port with me that I did this with as it’s for an older system but I can check one of the flat ports that I have with me tomorrow when I put my rig together to make sure it’s the same on all of them.
The 4mm for me was very tight but it does make a really nice secure fit and allowed for split shots.
Is the rear element framing the same in the WWL-1 and WWL-1B?