I get all three at the beginning of the season about half the time. I have no idea what determines who gets to be an impact player. I've had instances where i had 3 90 rated linebackers passed over for it in favor of 83 rated nickel back.
One year my punter was named the third one, but since my offense was so potent we never punted. So he loses it and then it goes to my kicker, who was already a high 90 since he'd been the starter the previous 3 years. Talk about lame.