Every load DMR publishes is per square metre of bed. In the first two flushes a bed makes about 10 g of carbon dioxide per square metre every hour, about 10 W of heat per square metre, and loses about 31 g of water per square metre every hour at 17 C and 85 per cent humidity.
So if you add a tier and increase bed area, you increase cooling, ventilation and humidification duty in the same proportion. The machine does not know you added shelves.