Would your GNSS antenna model “GNSS Multi-Band L1/L2 Surveying Antenna - TNC (TOP106)” improve drift as compared to your “GNSS L1/L5 Multi-Band High Precision Antenna - 5m (SMA)”? I am currently using the latter antenna, and drift averages 15 cm. I am using the GNSS board “SparkFun GPS-RTK-SMA Breakout - ZED-F9”. The magnetic antenna is mounted on your “GPS Antenna Ground Plate”. The antenna in on a rooftop with clear view of the sky.
Yes, you could expect it to perform a bit better (the TOP106 has ARP offset calibration data, the other does not)