The devil is in the detail.
£2.2 million including add ons is only good if the add ons are realistically attainable and don't make up a big proportion of the fee.
So £1.2 million up front plus add ons of for example £500k if Millwall get into the premiership within 2 seasons and £500k more if they manage to avoid relegation the following season. To me that would be a very poor deal and you would be unlikely to ever receive the add ons.
The whole thing smacks of an agreement between Hibs, Nisbet and Millwall made in January. The story coming from the player and the club at the time wasn't credible. As ever we were told half a story like we are being told half a story today.
The bottom line is Hibs will work to get the most money for the club, Millwall or whoever ends up signing him will try to get his transfer completed for the lowest amount of money and the players agent will work to get the maximum money for his client and himself.
Finally the player will sign the deal that benefits him most.