I have a lot of healthy Alba plants, so I prefer stem cuttings over leaf cuttings. A stem cutting only takes 3 weeks to take off. With leaf propagation, I believe that the more the bottom of the leaf is in contact w/ the soil, the better! That's why I plant mine more horizontally than vertically. The roots grow vertically, so by doing that, I ensure the multiple sprouts' roots don't become entangled. I encourage multiple sprouts by notching the center vein of the leaf(everyone knows this, but...). I've noticed by making a small hole in the leaf at the notch, it allows the shoots to grow up and thru the leaf as opposed to breaking thru it or going around it. With Alba I have used full leaves that were only 1" long, also cut a 6" leaf into 4 sections and everything sprouted. I would not use sections or small leaves for rooting Viridis. The larger the leaf and better condition it's in, the better the chances are for surviving and staying green until root growth. I think Alba roots better than Viridis because of the growth rate. A leaf from an Alba plant may only have to survive half as long as a leaf from a Viridis before producing. I've only had 2 Viridis leaves (w/ roots) and they died. I can't kill an Alba leaf without frying it. I have green sprouting Alba leaves that've been outside in the dirt for over a year! They've been thru freezes and under water for days. I think when a leaf gets rooted, it'll stay green and survive for a very long time. If your careful when removing shoots from the leaf, and don't hack it up too much, I think one could get 100 plants from a single leaf. One can get a LOT of plants going quick w/ leaf propagation. Enough to share w/ everyone and still keep your own collection growing.
One day I hope to take all of my notes and make a Psychotria propagation guide.