I think it's done internally and i also think DOSBOX "feeds" enough files to everything you throw it at. If you have problems, it might well be because unknown or undocumented file access is being done.

There is a problem with Stonekeep v 1.2 (patched version) - it wants files=15 and it doesn't run 🙁

Internally dosbox allocates files=100. Buffers=(something equally large).
I second eL_PuSHeR's comments; and might look into it a little later.