"make sure the fan speed when set to Auto is at least on the middle setting. I think there are 5 fan settings available when on Auto and when the temps are extreme you need to be at least on 3 which is the one in the middle. "
This.
My bad: as I have been driving BMWs since 1999, I thought I knew how the ac worked... If on 'auto' then the fan speed would vary as necessary to get to, and then maintain, the required temp.
On reading this in the above post, I had a play and realised why I was not getting the 'normal' experience of slowly increasing fan speed which would then settle down: there are five different 'auto' levels and mine was set to minimum.
Increasing it makes all the difference...
Still playing, but this definitely works for me!
Kudos to BGT3 for pointing out.