I don't know that size matters when it comes to propagating Echeveria. I have found some of the caruncles hybrids just won't produce new plants; they may root but that's about it. Some Echeveria will root and grow new plants from flower spike leaflets as shown in my compot pic will produce new plants while others won't. I have repeated tried to grow E. 'Red Ruffles' from its leaflets without success despite their large size. All of the E. chihuahuensis were grown from leaves from a stock plant. One of the most important factors, IMHO, is that you remove the leave such that you maintain the integrity of the leave end that was attached to the stem; you must remove it cleanly or you'll have ZIP!

Krystal, to begin, when you say "leaf cutting", would want more definition, i.e., did you just "cut" a leaf or did you remove it from the stem? Also, as Karen has said, yellow leaves won't make it, EVER! You need firm, green leaves. Allow them to callous for several days and place just the tips in a cactus mix or a perlite/turface mix and keep just barely damp; NOT WET. These are leaves I set up this past week or so as an example of what you could do. As you can see, I've got a couple of the E. 'Doris Taylor' that probably won't make it because they are a bit yellow. Here is a leave I just removed from the plant to show you the end and what you want. I am certain there are others who may respond to this thread that are successful growing from leaves they "cut" from the plant, but I'm not one of them. These are Euphorbia flanaganii that were growing on the crested form and I removed them about a 45 days ago and allowed them to callous for about two weeks before planting them. They are now rooted and pushing out new arms. Things like this are best removed by twisting them off, IMHO.

The rosettes are how it starts the flower stalk. It will eventually put out flower buds. If you cut it and plant it, it will still turn into flowers. The leaves from these stems can sometimes be propagated. Pups/offsets will usually emerge closer to the base of the plant.

You could try putting the sprout end of the leaf in dark, i.e under coarse sand or some other substrate. You could also use a rooting hormone, or a branching hormone. You can get both from a hydroponic supply...not recommending this, just saying it is an option. Rooting hormone is something I use a lot. it generally does produce roots in harder to root plants, and faster roots in those that are not hard to root. it also increases root growth on leaf props. But the issue with some reluctant echeveria leaf props is that many will produce roots, and then takes years to produce a plant bud. I have a few that are firmly rooted into their pots, have been for over a year, still waiting to see that little guy poke up.