It's a bit more complicated than that. There are 800-1000 runners that start when the gun goes off. The first 1.25 miles of the race is on wide city streets at a low incline and relatively low altitude. Now the vets of the race know not to go out too fast. If this is your first PP race, you are feeling great and it may feel fine to be near the front of the pack and wonder why most runners seem to be taking their time. After the first aid station (1.65 miles) the trail narrows to a single file and remains that way to the top of the Ws (3.02 miles) and parts beyond. At the first aid station, things clog up and you may even have to wait. Nothing frustrates a runner more than standing still while the clock is running.
Let's suppose you started too fast and are now in a group of runners that have much faster qual times than you. You notice you are breathing much harder than those around you. It is getting harder to keep up and the space between you and the runner ahead begins to widen. At that point social pressure sets in and you can almost hear the runners behind you silently yelling - keep up the pace, keep up the pace. So you step aside and let a few runners pass, but what do you do because the line never ends. I am a back of the pack guy and I have walked past a few runners on the Ws, with their arms hanging over the fence rails, gasping for air.
If this is your first PPA, compare your qual times to those of the other runners in your wave. If you are in wave 2, all runners will have a qual time for a half marathon between 1:40 and 2:25. As you run down the streets of Manitou after the start, take a look around; based on your time, should you be in the front, middle or back of the pack.