You're still assuming an even spread amongst the ones that are in that 1M. My point is it's usually hard to tell, and you should assume very few sites hold most

You're still assuming an even spread amongst the ones that are in that 1M. My point is it's usually hard to tell, and you should assume very few sites hold most visitors. Just keep re-applying the concept (of the 1m, 1000 account for 70% etc).