When I picked up a Discus 2c from the factory in 2005 and asked for advice about the optimal C of G for performance I was told about 15% forward of the aft limit and that further after "not only is it less safe but the climb will suffer" - which surprised me at the time but I stuck to it over the years wet and dry. I guess the same will apply to the 2a and 2b as the wing profile is the same.