Just the wallet. It is a complete waste. The air in there isn't stagnant, at least it better not be. The Co2 isn't going to just hang out in the bottom of the tent.
Then it would just lay on the floor and never touch a leaf.
Think about putting a drop of food coloring in water. Yeah it initially sinks but it will disperse.
The only way CO2 would collect at the bottom is if the air was completely still, no fans and no ventilation pulling cool in the bottom and exhausting out the top.