The Raymarine unit - according to Raymarine - is sourced from Sirius and branded Raymarine. The antenna supplied with it is the Shakespeare SRA-50 patch antenna. It has a very short ~4" pigtail with a TNC connector, then an extension of about 20' with the SMB male push on at the end. I believe that connector is nearly universal in Sirius receivers. Out of the Raymarine/Sirius (white) black box is e-net and RCA audio. The UI is done on the chartplotter. It does have a diagnostic page with a lot of stuff on it, mostly incomprehensible without some insider knowledge.
Most of my experience with patch antennas is GPS in aircraft. I have 6 GPS receivers in my glider if you can believe that. The patch antennas are almost all tested and rated with a small ground plane (like 4x4 or 6x6), however it mainly improves the upward gain and the noise rejection from below. We have issues in gliders at bank angles of say >30 degrees with the satellites dropping out, but of course they are all over the sky. I don't know enough about antenna theory to judge if a helical would be better, many people seem to think so, the gain pattern can be varied a great deal depending on geometry, and that particular one is supposed to be for offshore use so maybe low angles?
I wonder if you would see an improvement by tilting the patch antenna towards the satellite? Obviously not a practical solution, just some interesting data.