Easy q - click on group member portrait to 'assist'?

[kegsterino]

Hi guys

I set up duf to have portraits nice and big (like neeblers) and have enabled them portraits of group members + the whole frame to let me 'left click to 'assist' this group member'

Thing is - it doesn't seem to work - do I need to do anything else to make this function work? I assume 'assist' means that when I left click the group member's portrait, I instantly assume the target of my group member so I can help kill it.

What am I doing wrong?
(prolly something very noobish)
Cheers for any help
Keg