Inconsistent Clip Automation Behavior

I usually use track automation but have just started using clip automation again after a long hiatus.  I am finding that when auditioning it sometimes has an effect and sometimes not.  For instance, I draw a volume envelope in the track pane clip automation view to tame a nasty ssssibilant and, 9 times out of 10, there is no reduction in volume when I play it back, even if my envelope nodes are way down near -inf.  I toggle the R(ead) button and sometimes the clip envelope will kick in but sometimes it won't.  However, it does kick in if I "bounce to clips," which I never want to do until near the end of my fiddling.
 
Does anyone else have this problem?  Am I doing something wrong or misinterpreting how to use this tool?
 
Thanks,
Bill