I wish I had some experience with mats, so I could be more helpful. I'm sockless and matless.I need help.
So I decided to add a Redsea roller mat 1200, to get away from socks.
That's under normal operation with the return pump on? I would want the water level in the box to be just below the teeth.
If you take the gooseneck off the siphon line, I think you'll be pulling a vortex from the surface in your situation.
The system was working fine before with filter socks?