Mosquitos love damp -- and open, standing water. What sort of waterer are you using? Nipple waterers are the most effective at addressing water leakage causing dampness in the coop and don't provide any open/standing water to draw the insects in. What is the area surrounding your coop like - any damp/swampy areas or containers with standing water (as little as a teaspoon)?
In my setting it is not practical to limit habitat for aquatic life stages as they can fly from outside areas I can treat. Therefore most of my birds have to just deal with it.
A trick I have played with might be worth considering. Modify coop to operate like an arm pit which is a good scent trap. Make so birds in what approximates an inverted bowl where the roost is in the upper part of the volume. Then make so the repellent goes up into bowl where it is not dissipated as quickly.