I would be shocked if 26 is a comfortable number. 30, yes, but 26 ...shocked. I haven't seen the class stats for 18, yet I would guess it is on par with AFA, maybe even higher. Their stats are 30+ ACT/1350+ SAT.
Caveat, since the appointment process is geocentric at first (MOC), it could be that for your state it is a comfortable number, but candidates from MD/VA/TX/NY/FL/CA should expect a much higher ACT to feel comfortable. DE and NJ due to the proximity to USNA could also be seen as competitive too.
JMPO, and now throw it into the circular filing cabinet!
PS remember if you want to compare an SA to a traditional college, it is 16%. Basically, an Ivy league level.
I would also have him retake it because to have an 8 point spread between Math and Science makes me wonder if they had a bubbling issue on the exam. TThe science portion is a lot of graphing, and graphing is also Math. It might be just my kids, but none of them had more than a 2 point spread for those subjects. 8 is huge, and as a former teacher it would be a red flag why there is such a large difference.
Also, think about one thing...if it is truly an academic issue regarding Math and not bubbling....getting an appointment is one thing....commissioning is another. The minute they start classes, they will be academically behind their peers, and profs are not like HS teachers....they are not going to slow down the pace. Hire a math tutor now if it is an academic issue. A year from now you don't want them coming home for Thanksgiving and telling you that they are failing Math.