I am cutting rafters for a shed roof. The rafters will be 16o.c 2x6.
The rise is 3:12 (or 3 inches for each 12 inchs of run)

My question concerns the birdsmouth cut. If I cut a 1 and 1/2 inch
heel cut and a 3 and 1/2 inch seat cut, I am in compliance with the
code for Height Above Plate for the rafter. If I make this birdsmouth
cut, doesn't this alter the pitch of 3:12? Would I also have to alter
the rise in some way to account for the birdsmouth cut out of the
rafter?

Thanks for any assistance.

David