The real question is: how much does tutoring really helps as compared to simply prepping with free ressources?
Is it 5%? Does that mean you can't tie-break between two scores within 5% of one another? That's called a measurement error. No, this steel beam isn't 8 feet up to the micron.
I strongly suspect there are diminishing returns. You get the biggest benefit from knowing the material from school. After that, familiarity with the test (practice tests every weekend for a few months) will help the most (and tutoring is no substitute for actually practice the test). After that, yes, tutoring will help some, but again, diminishing returns.
Is it 5%? Does that mean you can't tie-break between two scores within 5% of one another? That's called a measurement error. No, this steel beam isn't 8 feet up to the micron.