A ranger at Zion told me my tent setup was the reason I slept cold, and I'm still not sure he was right
Two years back I was camping near Watchman Campground in Zion in late October, and it hit about 28 degrees overnight. I woke up shivering in a 20 degree bag, which should have been fine. A ranger walking by in the morning saw my setup and asked why my rain fly was cinched all the way down with zero gap at the bottom. He said I was trapping my own breath inside and soaking the bag, which made me cold, not the temp. So I changed how I pitch. Now I leave the fly staked out a few inches off the ground on one side for airflow, and honestly, some trips it feels warmer and some trips I swear it's draftier. My buddy keeps his fly sealed tight and claims he sleeps fine, so now I wonder if the ranger's advice was real science or just one guy's habit. I've tested it maybe 6 nights since and I can't tell if the difference is the vent or just the weather. Has anyone actually measured this, or is it one of those campfire theories that just sounds smart?