Thanks AlMitch
Yes, must be 8cm otherwise no focus. that octo was quite small, something like a mouse.
For WA I'm using the Nauticam WWL-1 and the short port, but the Inon you have should also work. If you're getting Nauticam housing, you need the short port in order to use the wide angle lens. The port has a standard M67 thread. Not sure with the Inon, but with the WWL-1 you have to zoom in around 35mm to avoid vignetting.
Note that with the short port, your maximum zoom is reduced to 70mm, as the lens cannot extend further (Like the RX100 M5), so you're limited to wide for the dive, unless you swap the WA lens with the diopter. I don't find it very practical... Nauticam advertises their bayonet system allowing you to easily swap, but where you put the WA lens for the rest of the dive ? ?