Just resurrecting this thread...
Someone I was talking to the other day suggested that the tailplane was modified on all 810 series (not just BMAT) due to the change in trim arising from the engine uprate for the 810. Geometric detail omitted from some 810 sillhouettes it seems ...
The reason - he suggested - for the asymmetry, was that it was cheaper to mod/certify just one side rather than both. The asymmetry having neglible effect.
What do you think - is he right?