They have to offer him a contract equal to what he's currently earning for the compo to kick in, doesn't matter what we're offering as far as I'm aware. If he chose not to sign for them and they refused to release him then he'd automatically be put onto a rolling weekly contract until his 24th birthday (or an agreement was reached, or the club decide to just let him go). As his 24th birthday is in July there's not much point in Forest trying to get compo if he's decided to leave, because all the clubs signing him have to do is wait until his birthday and then sign him. He won't miss a game for his new club, and they won't have to pay for him regardless of what the compo rules are for 23 and unders.