I have a feeling you're thinking about your tent completely inverted buddy,
The round holes with sleeves are usually for forced intake or exhaust, primarily used for ducts, located all around the tent,
The passive intake is the screened window with a flap cover, towards the bottom
The "standard" idea is to have your carbon filter in the top corner, ducted through a round hole, sleeve closed to seal it,
With everything else closed you will have serious negative pressure in there, sides caving in to each other,
Now you play with how open you'd like the flap over the screened window at the bottom,
More open, more air flowing back in, means less negative pressure
Causing air to be sucked up through your plant, passed the light, into the filter, and out through duct/fan, hopefully scentless
I'm not really sure how you expect to smoke a cig and then proceed to try and smell it though?
Good luck