42 square foot for 6 birds is going to be to your advantage as far as smell goes. The more space you have for them, the less it tens to smell. Given there are a lot of other variables. Chickens put off a lot of ammonia so a well ventilated coop helps that stagnant ammonia scent not to linger. Also what is the bedding situation in the coop and run? Deep liter or sand seem to be the two strongest methods for keeping odors down. A large part of it, will be your consistency with cleaning the coop, whether it be turning pine shavings, scooping poop once a day, scraping down poop boards and cleaning roosts, etc.
