What I was postulating is that probably the key driver of atmosphere is the percentage fullness of the stadium. From there you factor in the participation level of the crowd. When you have an average crowd of about 7k in a stadium built for 35k it really doesn't matter how into it the crowd are, when you're standing in the middle of the pitch the atmosphere probably isn't that great. That's no disrespect to YF, it's just a fact.
Sorry prof, I'm with FM here, size of population has no direct relationship to atmosphere, although an indirect relationship may exist. Look at the Green Bay Packers who regularly pack out their 60k stadium from a population of about 100k. By referencing the Bahrain game you are simply providing the exception to prove the rule. Yes, 36,000 going off in the RoF was a great atmosphere. 7k going off in the RoF isn't, and 7k going 'meh' in the RoF definitely isn't.