Have you considered post-processing services to determine the base location accurately?
You have to make a log of specific data for something like 24 hours at 30 second sampling rate. Then convert the product specific log into a rinex file and submit that file to some on-line service.
I’d done it with one Canadian site:
as well as an Australian site:
Read instructions carefully, submit your data and they should provide you your base location at better than 0.5 cm accuracy.