as far as testing goes, it seems that settings in CFG-NAVSPG (which seems to replace the old CFG-NAV5) do not apply at all when the receiver is in differential mode. e.g. it seems that the minimum satellite elevation is not taken into account, and that the rover is using all the sats that the base is sending.
I believe this is suboptimal as sometime bases have a very low mask, in order to track and log low elevation satellites for post-processing puposes, but you wouldn’t necessarily want them used in the RTK mode. (same thing for setting PDOP filters)
Am I missing something about setting an horizon mask and/or DOP filter at rover side with the F9P ?