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Its a difference of 3 feet, its not significant. 'Sides Lopez has had a 40+FB% before and and averaged 378 feet.
He doesn't have anything close to Alfonso Soriano type power and even the prime-Tejada (whos a step down from Soriano) had nearly double the HR/FB%. Still he makes better contact than BOTH of them, so you can expect a healthy amount of singles+doubles as well.
I'm just saying that 30 HRs in Safeco is really, really unlikely. That doesn't mean his bat isn't plus at 2B. Hes a very good bat for his position. 20 Hrs is nothing to sneeze at, and I think he'll do it again a season or two in his career.