James -
I believe we both share an interest in comprehending EM clearing more fully.  Your description of witnessing, as used in EM clearing, as increasing one's trauma capacity makes sense to me.  
A metaphor that comes to my mind is like afterburners that boost a jet to faster speeds.  John does seem to describe witnessing as something that boosts a person's ability to process adverse subconscious material better.  And, that would be an increase in one's trauma capacity.
But I am a lay person.  Hopefully John will respond.
-Dean