Hi Ying, and welcome to the course!
You can grow up to around 20-25% of the substrate weight over 2-3 crops if you re-soak the substrate (overnight in water) in between harvests.
We have found that it is possible to grow at least 2kg mushrooms per m2 every week if you cycle growing bags in and out of the space after just 2 harvests. The 3rd harvest is usually much smaller, so it is better to use the space for new bags than to maxiumise the yield per bag if you are limited in space.
hope this helps.
best wishes,
Adam