The 10 degree jib track rule of thumb is discussed in Arthur Knapp's old book 'Race Your Boat Right'. He gives the credit of it's origination to a sail designing friend who name I don't remember. But it doesn't sound too scientifically derived, it's a rule of thumb. He also talks about double sheeted jib rigging which is having a sheet attached to the jib or one of the jib sheet that pulls the clew downward as well as the regular sheet that pulls backwards (aft). I'd like to try this out one day.

Sail designs have really changed since many of these ideals were formed. Best to be skeptical and learn from experience and experiment.

Ben