For mooncakes, smaller duck egg yolk around 10 grams each one is highly recommended. If your egg yolks are larger, for example near 20g. Divide it into two halves and wrap in two moon cakes.
When pushing the outer wrappers, be carefully and slow down your process. Do not break the wrapper. If you do, pinch any small holes together. The time needed for assemble one moon cake should be around 1 minute even you are quite skilled. Be patient during the process.