DaveG28 , I know this does not resolve your problem but I have had the following experience here.
I started sponsoring one of our front running racers with a 2013 BX with ceramic bearings (note not the BXR with rossi ceramic) whilst waiting for the new engines SLS DI5 and SLS 5 to arrive.
To start with he loved the BX and said it’s an improvement everywhere over the smoking gun that he was using.(I leave that upto you to decide which engine it is, popular here and the UK)
I then handed him the new range SLS DI5 and SLS5 same piston and liner but different crank. Response has been " pls give me back my old engine" though the new one screams they don’t produce more punch in fact I’m told less!!But are really quick on the long sections but races are not won on the straights so it means little, and fuel consumption is less.
Though perhaps European tracks are longer with less jumps so this is a better option but here the racing is done at 2000m above sea level and probably a mixture of US and European style tracks would be my guess.
We also had one carb issue and one bearing issue .It must be said that RB's response to any issue I have have had has been excellent and I don’t think any manufacture out there will respond they way they do .If something is wrong they take my word for it and they replace.
In the pursuit to move forward and this coming weekend will be the first to do so we will now run the BXR SLS DI5 with the SLS3 piston and liner in the pursuit of fuel consumption and to try and get back the torque that has been lost. If this does not work out to be any better than the 2013 BX with ceramics I will then change all my imports to the BXR LS5 which is in fact last years BX and listed as the entry level engine for this year .
Also the kind of consumption you are getting with the SLS5 is the same as we experienced and the consumption with the older BX(2013) was in the region of 9min at the altitude mentioned .
All engines were and will be run on the 2097 with medium header with 7mm restrictor,i have only ever had problems running a 6mm.

I will give feedback on our findings 18th of this month after the 3 national .
Also the above is my opinion and is formed probably under different conditions to what you would experience in Europe.