Air circulation

Your totally fine man. They look great! What's your humidity at? If it's not over 65 then your totally fine. And if your starting flower just watchcit doesn't go above 55 to often while it's packing it on. Otherwise plants look good. Not evidence of them being lacking in air flow.

There is an advantage in air circulation if you add a fan below the canopy, but it makes the CO2 -bags pretty worthless if the airflow is going upwards. But when it comes to preventing humidity, mold, pests etc. it's a great thing to add. In my opinion your plants are not that bushy that the extra fan is at all necessary, it looks like there's pretty much room beneath the canopy and the airflow is good enough.

Yes there would be an advantage to placing the fan underneath the canopy if not much air circulation is there. The fan could help keep powdery mildew/mold from growing while also helping keep the inside of the plants environment steady with the environment that's at the top of the canopy.