You should try to see what R thinks its R_HOME (or RHOME) is. Try to run
R RHOME
that should print the value of RHOME and exit.
Alternatively, from the R command line
Sys.getenv("R_HOME")
I think R will read the startup and conf files from $(R RHOME)/etc/
Maybe it's not the location you think it is... Hope this helps
Regards