It never provided any ventilation before in the "vent" position--at least none that I could ever feel. 15% was ideal for parking, but they got rid of that because some folks couldn't figure out that you weren't supposed to drive when it was at 15% (caused a whistle) and whined to Tesla, so now 20% is the minimum useful opening. Unfortunately, that's too much unless you have the heat shields, then it's okay.