That’s not it, running the latest (2.4.3 b28).
It really is a weird one how regardless of entering a manual base location in RTKPOST the .pos file spat out has a different %ref pos (assumed from averaging or else). Yet if I take this %ref pos and subtract what I know is the real base location, then apply that to a processed set of data over another known location I get a great xyz comparison…
Ultimately, RTKPOST does not recognize a manually inputted base location.
I also had a play at editing the ECEF pos in the bases .obs file to see if I could convince it using the header information. That did not go so well.