D'oh! I don't know how I missed the sin beta part. It is very clear in your write up. I apologize for my obtuseness.

I am still not sure about the 1/sin gamma, though.

And yes, pacificaslim, it does have some real-world significance. If you don't have the 1/ sin gamma term, MA is maximum where the straddle cable is perpendicular to the cantilever arm, as conventional wisdom says. However, this model says that MA is always maximum at minimum yoke length for arm angles < 90 degrees; MA is constant at any yoke length for arm angle = 90, and is maximum at maximum yoke lengths for arm angle > 90. If you followed this model, you would set up your brakes differently than conventions and manufacturers recommendations.