I'd like to know where you heard about this and come up with that calculation, as I cannot find anything about it whatsoever. Further, using your calcuations for a second here (more on this in a second) when you talk about something like 950mb, you are talking 10mb difference -- that's significant, and I'd think it'd be more widespread or commonly known if such were the case.

Edit: where did you get your values for sin(40) and sin(60)? You can use a calculator to compute those, just ensure that you are in degrees and not radians. There's nothing weird to it, and calculators weren't built with those functions in them just for geometry. In any case, sin(40°) = .643 and sin(60°) = .866, making the ratio between them .742, or resulting in 1/4 reduction in the pressure. Something smells very fishy here.