That advice from Revisor is very, very good! I would suggest not taking the advice as a precise instruction. In practice, the precise angle isn't important - what is of importance is to focus attention on good contact with the edge of the razor on the stropping surface. Without bearing down on the strop, raise the spine so that it barely skims the surface or floats above it just a tiny bit. One millimeter, two, three... makes no appreciable difference. Ensuring that the edge and not the spine remains in contact during the stroke can make a world of difference in how sharp and smooth the edge becomes.