Looking through the code, here are two details that might qualify as clues...
1. The current file has to be identified as an "asbmain" file type, which is based on the extension being listed after "asbmain:" on the --langmap= line in the \ctags\additgionalLanguages.conf file ...
--langdef=asb
--langmap=asb:.bas.bp.bpi.bsi.cpy.def.fnp.gen.get.lsx.map.mps.opn.sdf.siz.stru.sub.upd,python:+.pyw,asbmain:.bas.bp
--regex-asb=/^\s*function\s+(.*)\(/\1/f,Function/i
...
2. The logic is slightly different depending on whether you are working within a Project or not. In the Project case, there should be a file %TEMP%\APN\<pid>\curproj.lst specifying the project attributes and a \Customer Projects\includes directory containing .lst file listing the ++includes associated with each main program in the project.
Otherwise, there should be a directory %TEMP%\APN\<pid>\ppg\includes with a similar list.
I usually start with a Project, but then once the Project is created and selected, from then on I just use the Workspace method of saving/retrieving my context between sessions. (The Workspace contains the Project.) So I'm generally always working in Project mode.