I think it's several things, not just one.
Her jumps also aren't simple, with no steps in or out, which makes them more difficult but also can limit size but yes, smaller jumps are easier to control.
Then Eteri practices the philosophy of multiple repetitions. You mess up, you do the whole program all over again. This is good for consistency but at the same time, difficult for the body, especially as one grows older so it's good for Zhenya she's moving to Orser who is a proponent of quality over quantity as that'll reduce the injuries.
But another thing that isn't often mentioned is her mental strength. I've said it before, I'll say it again. Her biggest gift is her mental strength, her head. I can only think of Plushenko when I think of this combination of nerves and incredible drive to win.
Many girls have average jumps, that are flawed here and there yet we don't see this consistency. It's not that easy to put your finger on one thing, and go this is why but if I had to, I would actually say it is her mental strength that helps her the most, in a combination of several things.