Simon - If the programming is similar to my Futaba FF9 - set it up in "Flapperon " programme and you can adjust each servo accordingly,
the "Flapperon" programme automatically mixes them.
If required, direction can be reversed in "Reverse" programme.
When 2 aileron servos are fitted I always set them up in different channels so each can be adjusted seperately.
Look forward to seeing the "Waco" flying.
Colin.