He wants things both ways...
To be paid now, and also to cash in later if the cap continues to grow.
Cant usually have things both ways in a negotiation, and I'll say it yet again, Prescott should sign as long a deal for as much guaranteed money as he can get right NOW.
Betting on everything else to go his way is fools gold.
Sure, all of it MAY happen, but you cant have all you want in the short term, plus to be protected and cash in later as well.
This agent is taking him nowhere, except possibly to where fans are against him.