Alan:
     I believe you hit upon the actual reason they seem more defensive now
that they are established.  They have something to protect.  One thing struck
me from your description.....you never mentioned smoke.  Did you not use a
little smoke when you work your hive?  If not, try using about 3 good puffs
into the entrance and lift the lid slightly and give one good puff under the
lid.  Wait about 30 seconds to a minute and you should notice a dramatic
improvement.  Good Luck.
 
Gordon