It's been some time since I did this, but yes, it's mostly the correct height + keeping the hand steady when the drop falls. I think getting the height right is more critical. You need enough time to have the drop cool down. On the other hand, higher means also larger impact which can splat the drop more easily.
I would imagine that could be solved by keeping the water at or near a boiling point; breaking the surface tension of the water while still being cool enough to let the tin completely solidify.
