802.11N Range with G devices active?

Hi,

I'm having trouble getting signal in my room using an airport Express 802.11G router. I understand that if, say, an iPhone connects to an N network, every device has a slower connection speed (even an N MacBook). What about range? Does range decrease, or does the N computer get increased range?

Also, do Airport Expresses have a smaller range (weaker antenna) than other routers? Do I need a better router to create the network?

Thanks