Disagree here. I use his exact build with the airflow on the second smallest hole with tons of vapor. His issue is something else. My guess would be not enough cotton/incorrect wicking or incorrect coil position.
Without any photos of the build it's harder to diagnose. You are correct that it could be too little cotton, thus feeding too much juice to the coil which heats up but doesn't vapourise, which leads to small vapour production and hot chamber. However, he should have noticed significant gurgling or leaking when refilling if that was the case.