You need to pick and choose the segments that you want to attempt a PR on and do a hard interval type effort. You can't just expect to go out and ride your bike at a decent clip for 20+ miles and do well on every Strava segment. Even racers don't go balls to the wall the whole time they're on a training ride. And yes, it helps to have a nice tailwind if you're going to place well on the "leader board."