Thanks for the excerpt.
I'm afraid that Tre wouldn't take a declining deal because if the Spurs want to re-sign him at the end of that deal, and if the Spurs are over the cap at that point (as they likely will be), under the current CBA Tre's new deal could only start at 108% of the last year of salary. An increasing deal instead of a decreasing one makes a lot of difference over those 4 years, and Tre will be 27 and looking for the biggest contract of his career.
Maybe the sides can compromise on a flat deal, but if I'm Tre's agent I'm telling him not to take a declining deal. It would take a lot more up front to compensate for that.