Mike, I really have not get the 'chem' of the soil yet.. I use whatever I have or can put my hands on....even found myself cooking garden soil in the oven to be able to use....did I say that? I found that what seems to work best for me, is to put crumbed styrofoam at the bottom of the cup and a light soil, so whatever is in it that works, even pine needles did ( or crumbled styrofoam)... and after I put in the cup, I try covering the stick completely to hold that limited moisture needed so, may be used up newspaper or moss they were nesting in during rooting process, once leaves appear, I remove that loose materials (pine needles, paper, or moss) to allow the leaf to process the light , but then, there are roots...
when I prepare the cup, I put styrofoam at bottom and fill it almost full, add water and with 2 fingers, I open a ft hole in the middle. the moist soil stays on the outter side I put the cutting in the middle of the hole and fill the hole with soil/perlite (50/50). so, around the cutting itself is a very porous matter - also I make several holes on the sides of the cup.