Huddersfield Town have to pay Bradford City £250,000 - should the Terriers achieve promotion this season.
The Bradford Telegraph and Argus claim the Bantams have a promotion clause built into Wells' contract, which the Bermudan signed in January 2014.
The deal was initially worth £1.3m, but Bradford have been entitled to a further £325,000 due to performance-related add-ons in the deal.
And the Bantams will receive more if the Terriers go up and will also receive a percentage of the fee if and when Town decide to sell Wells on.
However, should Town go up, the £250,000 owed to Bradford would pale in comparison to the cash received by the Terriers.
Last season, Deloitte's estimated that Sheffield Wednesday would have received around £170m should they have achieved promotion to the Premier League.
Although that figure would likely have been smaller for Town last season due to the capacity of the stadium and size of the fanbase, the amount of money earned by the promoted side is increasing each year.
In 2006, Deloitte's estimated the play-off final was worth around £40 - a quarter of what it was believed to be worth last season.