I've finished building the spars but still have to glue in the strut fitting support boards in the center of the wing. The plans call for 30.5 deg on all spars. My hand calculations and cad drawings both show the angle to be either 39.4 degrees depending on whether the root fittings will be on the top or bottom of the spar. This takes into consideration:
3 inch dihedral on the end of the wing
Root fittings on the bottom of the spars (see attached)
Mount plate similar to attached image (see attached, credit to Scott Weinberg)
The connection will be the strongest if the force vector is in line with the strut fitting. Has anyone else changed the angle?