A draft blows on your chickens, ventilation allows air flow to move heat, ammonia, humidity out of the coop. In summer you can't have too much air (unless you live in extremely cold place). I would cover the bottom vent and use a poop board under your roost. Your top vent is a little too close to your roost, but maybe you could close off the bottom half of it or redirect the air flow so it doesnt blow down on the chickens.