This puts the bid below the £14.75 on the table from rival bidder Comcast.
Some observers had expected Fox to increase the offer for the 61% it didn’t already own.
The City Code on Takeovers and Mergers requires bids to be in by August 9, 2018.
Sky has acknowledged the offer and says its independent committee would respond within 14 days.
There have been changes to the method through which Fox wants to take control of Sky.
Rather than the shorter Scheme of Arrangement, Fox is now planning a traditional takeover.