Jerry
Nelson is right.
Since humidity (Moisture) and temperature helps rooting, shooting, rot and mold, so think of ways to keep the bottom side relatively warm and moist while the upper part is relatively cool and covered to avoid drying up of the cutting.
Sometimes ago I saw a write-up on a small fridge size equipment for rooting of cuttings on the same principal i.e. keeping the top portion cool (but humid) and the rooting portion warm.
Beside, the nature of the cuttings also has a factor. My cuttings are from plants grown in Zone 5 summer which may not yield ideal cuttings for all plants. The ones near the south side wall seem more lignified (where they ripen too!) than the ones in the open