RE: OMP Yak build
I gotta hear all of this. This plane is on a short wish list.
I think the 89.5 degree angle is to offset the fact that building the wing with this taper would otherwise require the tip to be supported somehow, perhaps on raised jig tabs. With the tip down on the board, with the root, all ribs must be canted to keep them vertical once the wing is squarely mounted to the fuselage. If you don't do this, when you mount the wings to the fuselage, the ribs will cant 0.5 degrees towards the fuselage, and not have the proper geometry.
smallfly, I'm with you, my head hurts...