Unlike a standard 2v icosahedron based geodesic sphere which has two different dihedral angles the mono-dihedral version has been augmented so that all the dihedral angles are approximately equal, I say approximate because it's not possible to get the calculations exact so we work to a tenth of a degree and call them roughly equal. To build the mono-dihedral 2v we start with the Rhombic Triacontahedron then perform a 33.5% truncation to produce a truncated Rhombic Triacontahedron. The dual of this polyhedron is the mono-dihedral 2v icosahedron, Rather than two dihedrals of 157.541 deg and 161.971 deg as in the standard 2v icosa it has dihedral angles of 159.859 deg (pent) and 159.93 deg (equal) respectively. The diagram below shows a mono-dihedral 2 frequency icosahedral sphere which looks just like a standard 2v sphere despite the geometric tinkering.

Chord factors for this geometry are: 0.558609 for the pent. 0.636762 for the equilateral. This geometry is only practical when used with the beveled frame method to reduce the variation in bevel cuts, other build methods that don't use dihedral based construction methods won't find any benefit.