I don't get you.Remember how Hayward would have gotten less if he maxed out the year before?
Max salaries are a percentage of the cap.
We are assuming Kanter has the potential to receive a max offer sheet, which will be more next year if the cap goes up.
Players sign contracts with $ figures, not %. They sign as per current cap regulations, not future as salary cap is established annually. If Kanter signs max deal this year it will be 2015 max which will be set coming July and won't become 2017 or 2018 max later on.
Obviously, if you are after max than the more you drag out the signing the more you can get as max contract goes up with the cap but once you signed, future cap increases are not your concern.