Another quick observation, you mentioned 0.85 and 0.9 afr, these are Lambda figures not afr.
1.0 Lambda is 14.7afr, so at 0.9 Lambda you are seeing 13.23:1 afr when you want to be at 12.0:1 max. The ideal Lambda you are looking for is 0.80 while on boost and up to the red line, it can go as high as 0.82 but certainly no higher, especially at 1.2bar.
You are probably sick of thinking about it by now Simon and the last thing you need is me babbling on at you, but as you know i've been down the same road and i'm just trying to help. What Nathan said earlier is a good idea, if you get the CIS test gauges you can set up the fuel system yourself, if you also purchase the LM-1 or LM-2 from Innovate Motorsports with the necessary sensors you can precisely log your RPM, Boost and AFR on a lap top live whilst on the road. The CIS gauges are cheap and the Innovate stuff will be good to have hooked up whether you are sticking with CIS or going EFI.
My guess is that you need to add some shims in the fuel head to raise system pressure, your pumps will run at over 100psi, most people see too much fuel at around 90psi and end up dropping this down to around 80 or so, if you have a look at your system pressure i bet it's around 80, when i ordered the fuel head i was around 415bhp and Stephen at Imagine knew this, I could ask him what he set it at but you need to check it for yourself and adjust it for more.
The chap at DSA seams like a really nice fella but i didn't get the impression that CIS was his specialty, I wish you all the best with it mate!
JBL