Hatch gives less meat than they should when they drown if there's meat on the ground and there's an open space above them

First put the hatches like this and wait for them to drown

You will get 3200 kcal of meat which is 2kg per Hatch

Add another batch of Hatch without removing the meat

After the 2nd round of Hatch drowns, you'll end up with 4800 kcal of meat which is 3kg

The Hatches on the bottom that were enclosed dropped correct amount of meat, 4kg in total per Hatch.