On Gmail, why does it sometimes fit on one page, and why do I sometimes have to scroll all the way across my inbox to see the other side?

OK so on Gmail lately, sometimes I can see my contacts list (I have it set to be on the right side) without scrolling. But other times, it chooses to be difficult and make me scroll. This happens when the inbox is empty, so it has nothing to do with the length of the subject line of emails. It’s quite annoying. I’m using Google Chrome if that has anything to do with it.