I've been mucking about with A4 on both this laptop running Mac Sierra and also on the iMac running 10.7.5 (I copied the save file over for direct comparison) and I think Difficulty is borked, it no longer works. Doesn't seem to matter whether I'm playing Torment or Casual.
I started playing Hard and found it too easy so went to Torment and there was no difference, enemies were just as easy to kill and just as ineffective in dealing me damage.
Has anyone else noticed this? Is there anything I can do? Running v1.1.2 on both machines. That it runs on both machines with radically different OS's a testament though so this is only a minor query, not a big complaint.