Could it be that the Emlid RS2 is not able to handle antenna type corrections in real-time? I noticed this strange behaviour when changing to an EUREF station (which broadcasts ARP + antenne type), so I tested it with two different data streams from the exact same reference point. One is broadcasting the APC position with NULLANTENNA in RTCM message 1007/1008 and the other one broadcasts the ARP and includes the antenna type.
If I measure a point in Reachview, the resulting elevation in the base position differes by exactly the phase center offset of the used base antenna. Is the RS2 unable to use a lookup table in real-time apply the antenna corrections? I did the same test with Leica equipment (GS14) and obtained the correct position.