As I said, this is going to be a lot of trial and error and may take some patience to dial it in. When doing this, make only one change at a time and evaluate the results before making another adjustment so you know what worked and what didn't. Hope this gives you some ideas to start with in regard to setting your equipment the best way possible to accommodate your knee problems.
Thanks for your advice Snowolf.
I'm at 18 / -12 and that seems pretty comfortable. I also got some spacers for my inner boot and it now supports my ankles much better.
In fact I would say that 80% of my issue was related to heel lift and lack of support in the boot.
Once I had the ankle pads put in I was a lot more confident; my body movements were much less exaggerated and I was steering with my feet. I still have to watch my front foot but in short it's much better.
It is also much better for switch. I have gone from being virtually unable to ride switch to being able to do slow ground 360s and toeside turns in switch.
Unfortunately I twisted my bad (reconstructed) knee doing an ollie the other day on the mountain
It's been 3 days and it's getting better; I can still support my body weight so I don't think it's anything more than a Grade I ACL tear, ie a fairly mild sprain. Time will tell but I hope to be able get out there again soon to keep developing my skills!