I believe the issue is the composition AND the orchestration. To me, the two are inseperable when you are dealing with a soundtrack (dialogue, SFX, room tone). The logic is that sonically, you're dealing with a (more) crowded canvas as compared to just music by itself. For example, an outdoor scene in a thunderstorm will require slightly exaggerated orchestration as well as a more simplified overall sound (composition) to allow for the elements to be mixed together with maximum volume and clarity.
I have had great success using these two guidelines:
1. Treat the dialogue as "melody." Not melody in a literal sense, but from a textural/arranging standpoint. Counterpoint can work behind vox but slower is better. Watch range when orchestrating as to not crowd the vocal register.
2. Finding the holes for thematic or high contour material (mentioned somewhere above) a la J.W. musically validates the lower profile underscore.
The result is a natural dynamic that eliminates the need for aggressive ducking, etc.
Clark