Lack of co2 and fresh air

All I can add is maybe keep in mind too that the plants will grow even more once flipped to flower. I’ve heard of some plants doubling in size or more after flipping to flower. Maybe someone more experienced will chime in on it. They look great either way so good job!

I've rotated the plants for now, first thought was genetics but when I was fixing ventilation in room, the route in which the air takes just crossed my mind. In the mean time I thought I'd ask the question if it's possible in a tent to actually have corner excluded due to the setup. I was venting into the room so had its own issues. I'm now venting straight outside and a window slightly cracked open for fresh air into the room. Temperature has changed quite a bit. Within the room has dropped from 25-27c to 20-21 and inside tent from 25-29 to 22-25 during lights on lowest inside drops to at lights off is 19C at the moment. We'll see what sort of difference that makes. I'm trying to get good flowering conditions now before it's s scramble. I was planning to flip I'm probably a week or two but the runt is giving me second thoughts. Other 3 have 3-4 nodes on main stems after topping. Gelato is slowly pushing out the second. While the lower side branches are matching if not beating the mains in height.

If there's more air exchange under the leaves of one plant vs. another. The frequent air exchange plant will grow faster. Your tent has vent flaps on the bottom of the walls. Some have one, some have Three. I keep 1 open which is away from any light source. The plant that sits in front of it dries out faster than the other's, because almost all of the intake air comes through it. Oscillating clip on fans are awesome. They take up no floor space, and are small in general, and work very well to move air around the garden. The co2 immediately under the leaves gets used up quickly, and if there is no fan moving the air around the room the plant's growth becomes stifled. That's why it's recommended to exchange the entire volume of air in your garden every Sixty seconds. VPD is what you want to shoot for because that affects the entire garden equally. The higher the humidity in the environment, the more atmospheric vapor pressure against the leaf's Stoma. The pressure against the leaf determines the plants ability to transpire and at what rate. Weed grows in typically warm tropical places. Keep your temps around 80F and your humidity during veg to be 70% humidity. Transpiring is reduced. When flowering, a temperature of around the same 80F but humidity reduced to 50% More transpiration.

I'd say it's just down to the genetics . It's just the runt of the litter . I usually get one or 2 , especially with autos . They grow small but can produce some very nice bud .

I've noticed the opposite. The ones directly near fesh air grew slower. It could be a different pheno that is just less vigorous. Although the fresh air could be playing a part. other things could contribute. Starting with that plants watering needs, if you may of over or under Watered the plant it could of been the cause. If not over or under Watered or fed.. and if we remove the possibility of a slower less vigorous phenotype, and only attribute this to less CO2 then you could rotate the plants giving them equal amounts of fresh air. You could open other vents allowing more fresh air in, you could also add supplemental co2. Either exhale bags, or one of the other ways to add co2, although those are expensive. I would rotate the plants or open more vents, and would make sure to not over or under feed or water. Goodluck growmie

You can try rotating plants( not a bad practice anyway when they're small enough to be manageable) but it's probably just because they're different strains with different grow rates. As they get bigger you'll either have to manage the height of the tall ones or give the shorty a booster seat.