This is incorrect. I have placed ads on /r/postmates, which is a small subreddit. You can't target some of the really tiny ones because they lack volume. I thin

This is incorrect. I have placed ads on /r/postmates, which is a small subreddit. You can't target some of the really tiny ones because they lack volume. I think it also "remembers" which subreddits you've visits, and also uses that to target. That said their ad targeting system is quite bad in other ways.