They came today to finish off the install. I requested them to put the outdoor unit above the existing one via a stand originally. I didn't want it braced into the external cladding in case it resonated and annoyed me inside the house.
I do admit, this is pretty ugly (industrial look), and looked cleaner in the marketing pictures, but oh well. Function over looks hahaha... 

Had a talk with them about our cooling problems. The bypass damper still needs replacing, as he said it isn't fully closing. So that I suspect means I'm being robbed of some throughput. Probably not the sole reason for the performance issues.

He said he will try increase the static pressure when he comes to replace the damper. I did tell him about the fact the unit isn't turning off when at tempt, but will do more testing to be sure.

I remember my mates place in Brisbane, Australia, when he turns his central heatpump on, the return grille is super loud. I don't know what setting he had on, but I suspect it's high fan speed?
When I have high fan speed on, it's louder, but it's still very much a low background noise, so maybe my static pressure really is way too low? Unless my mates setup is abnormal (it was a much bigger house).

Here's a picture of the setup in the attic. Haven't had a walk around yet, but probably will do when they come around next.