So after having spent some time testing out the scopes in a variety of settings and comparing with the exact range as calculated with map updates "on", I can say, the ranges are right on (running at 1920x1200 w. 8:5 patch). The range as calculated from the scope is usually within 10% of the real range, although that difference has more to do with my ability to guesstimate the actual mast height against the horizontal bars.
the formulas which I use are the following:
observation scope:
1.5x - MastHeight x 100 / horizontal bars = Range
6x - MastHeight x 400 / horizontal bars = Range
Attack scope:
1.5x - MastHeight x 50 / horizontal bars = Range
6x - MastHeight x 200 / horizontal bars = Range
excellent work.
