My seedling mixes have become more lean as I have become more experienced, also. Now I use probably about half sand, 1/5 potting mix and the rest varied sizes of grit. And more often now, I'll put a quarter inch layer of almost pure regular potting mix at the bottom of the pot for two reasons: 1) to prevent the excessively sandy soil from falling through the holes, and 2) as a reservoir of moisture for the mineral soil above. I am also imprecise in my mixing methods, and exact proportions are never the same. Depending on the seed, I use a surface grit layer of grit, on up to a cm deep.
In respect to the leanness of my mix, yes, I think I am on the extreme end. For myself, I seemed to have found that since I mostly germinate seed outside with the normal season, with more moisture retentive mixes I would sometimes get seed germinating at the edges of the pot, rather than all over the surface. This I attribute to the faster drying of the medium at the periphery.
