So I have a Corsair 4000D air flow, and the top of the case is like full of holes to allow airflow (with a dust filter on top of it).
Thing is, I put the case more or less below where my hand is touching the mouse, to the right of my feet.
And, well, I could wash my hands or otherwise have my hands be slightly wet at some point, so I am afraid, those holes would be easy for a drop or two of water to fall down on the PC components.
Are you using top fans? If not, cover it so that the air is simply sucked in the front and pushed out the back.
I am not using any top fans, no, only front and back (and bottom if we include PSU fan). Thought the vent on top could also help with airflow though, not sure.
You want airflow to be like a wind tunnel. Open vents without fans hurt cooling, not help it.