That error sounds a bit excessive. Are you absolutely sure that both units are operating in the same geographic system (WGS84 for the Reach units)?
Do you get the same rough offset from all the 10 stations in the network ?
RTK or PPK ?
I made a test recently, but that was for the relative precision, but the absolute precision is, given good relative precision, dictated by baseline and base station: Evaluating relative repeatable precision of the Reach RS+ - #18 by wizprod