PVsyst only treats the mix of 2 orientations on a given MPPT input.
If you have 3 orientations, you should define an average between two of them. The results will not be very different.
When do you mean with average between them? Lets consider an extreme case where we have 2 orientations: -90S and +90S. The average would be 0S (??) but the result couldn´t be more misleading.
I am trying to compare mismatch losses of central inverters and string inverters for minor differences in orientation.
Thanks in advance.