I have no experience with merit money, but it is generally understood that the merit scholarships go to the very top of the applicant pool, with attention given to grades, SAT scores, and leadership positions.
From Lehigh's website: "When awarding merit aid, we take a holistic approach, looking beyond the numbers related to academic talent alone. We look at what a student contributes outside the classroom and also consider recommendations and personal essays.
Some of Lehigh's scholarships require an additional application; for others, all students are considered just by applying to Lehigh, so be sure to check the application checklist for a summary of steps you need to take in order to be considered."
Lehigh University: Academics: Undergraduate Studies: Merit Scholarships
Since FA is a big concern of yours, your son may want to retake the SATs (2100 is often a magic number, and he's so close) and then make sure he applies to schools slightly lower on the rung that offer good merit. There's a thread somewhere on CC about schools that offer good merit aid. You might want to do a search.