I'm fascinated by this...can we develop the thread a little and ask someone to explain why it is normal, as it seems to be, to have either positive or negative decalage?
Why does it help to have one wing on a biplane providing more or less lift than the other at any given AoA? Could the same effect be achieved with a different airfoil section on each wing?
Are the centres of lift of the two wings in vertical alignment in level flight?