I dunno.....I put a big oversized vent in mine [about 8-10" wide 3" tall opening] and you can see it working with a puff bottle inside the tent.
By comparison, the vent in my old SL5 was worthless using the same test.
I've only used my tipi in 2 spots; a swamp in Alaska on a drop camp moose hunt....and the high mtns in Montana....from what I've seen, I think a good vent makes a difference.
As a side note, the orientation can actually matter. Wind blowing against the vent inhibits air movement....but on the leeward side....it can help suction air through the vent with the eddy current. BTW, we had a day of 60 mph wind in Alaska with my tipi pretty exposed and it shed the wind like nothing I have ever seen!
Heres mine but I don't think these pics show the vent...
View attachment 78283View attachment 78284
Edit; oh yeah, the one Ak pic shows the vent being compressed on the windy side [always blowing in Ak] So that grass out in front of my buddy is deceiving...its actually growing in water about 4"-12" deep that goes in under the tipi....no dry spots to pitch within a 1/2 mile of that spot. Why there, we spotted moose from the air on both sides of that lake.