QUOTE(Eutopia @ Aug 21 2009, 19:17)

You probably have some equipment that increase the proficiency. Go to your equipment screen scroll down twice and check + supportive magic.
QUOTE(cmal @ Aug 21 2009, 19:17)

There's another element in the equation. This element is a constant that is increased by 0.1*prof. I didn't run the numbers properly to determine how that factor is increased, but its the only way the math works.
Man do I feel stupid.
Anyway, I don't have any +prf to supportive, so...
3 * (x + 0.1*15.11) = 7.5
Apparently x is about 1.