Q: 16 bit code calling 32-bit DLL on Win 3.1

Is this explained anywhere.  I am trying to use a 16-bit DLL library
that supposedly crosses over from a 16 bit environment
to a specific 32-bit DLL written in WATCOM C. (maybe they are
 too lazy to rewrite it for older 16-bit environments).
It seems to work randomly and probably has some problems with

Does anyone have any tips, suggestions or references on how
this is supposed to work?

Please email as well as post