Guys I'd just like to reiterate there is a singular "fast heat" for each event. I was involved with the heat design process in 2012 when I worked for Gags. The goal of Oxy is for as many athletes to run standards (be in Olympic or OT) as possible. In order to do this they spread the faster athletes among the heats for a few reasons. The easiest explanation is so there isn't bunching, heats string out better when you have a larger range across the field. With faster athletes in multiple heats they can tow other runners to standards. Also by doing this the focus is essentially more on time trialing than head to head racing which instinctively would involve tactics and slow the races.