Unable to get GROFF_ENCODING to seep through to sourced subfiles

[Dorai Sitaram]

I have GROFF_ENCODING set to utf8, but this only works for the main file 
processed by groff, not to any subfiles that are sourced via .so .
Giving the -s option to groff to force a soelim doesn't work either.  
Adding the -k option to force a preconv, whether before or after the -s option, 
doesn't work either. (I think regardless of the placement of -k and -s, -k 
happens before -s, hence the problem? Perhaps -k should be forced to happen 
last?)
What does work is
soelim mainDoc.ms | preconv | groff ...
but it would be nice to avoid the pipelines with either options and/or 
environment variable.
Thanks--d