I think the document refered to have some grammar problems and miswrittings that are unintentional

Their base models seem to be okay but some phrases are open to multiple interpretations

I think the updraft comment intends to say that a sloop rig can point higher than expected when adding the optimal angle of both individually. Which it does.

I don't see uni rig pointing 15 to 20 degrees higher when a normal battened sail needs about 20 to 25 degrees to operate fully powerup.

The difference between unis and sloops is more in the 5 to 10 degrees.

I think no monohuller would seriously claim that a sloop points higher than a uni-rig.

The document however does stated that the first improvement would be adding a jib. It does however ot say that the gains will come from pointing higher. It leaves this point open. I think the intent here is to say that adding a jib would improve power enough to attain a better VMG by going faster despite the fact that you will point lower.

There is definately more material on the subject that the main makes the jib more powerfull than its size would suggest. In stead of teh jib making the main more powerful by a slot effect.Both Bethwaite and gentry are exponents of this line of thought. Net result is of course the same.

Colin, did you had a better VMG than the sloop when doublehanding the uni-rigged Dart 18 ?

Wouter