A 1.5 Fair is not actually a half grade in their opinion.
https://www.psacard.com/resources/gr...andards/#cards
Click on the box about half-point grades. It states "For example, there will not be cards graded PSA NM-MT Plus 8.5 OC or PSA EX-MT Plus 6.5 PD since the half-point is reserved for high-end cards within each grade."
So a 2.5(MK) is not possible, and actually won't fit on their Pop Report charts the way they're laid out, since there are separate fields for + (half-grades) and Q (qualifiers). However, since 1.5 FAIR gets its own column, it is not actually a half-grade and therefore, I guess, PSA allows qualifiers on them.