I think I figured it out.  Companions can’t “dodge” attacks like regular players can.  If there’s a giant red spot on the ground, companions act like cats chasing laser beams.  Smoosh.  This big boy killed me twice before this video.  He came close a few more times as you can see.  Pretty sure I’ll be changing my skill lineup for the next boss.

I’m 52 now (linear levels, about 4 per night), so only a few more levels to go.  2 zones methinks.