If you would like your .270 hitter to hit within 10% of his real life stats then the bound is not .260 to .280. The limits would be .243 to .297 (.270 * 0.1 = 0.027)

also look at more than batting average. Brian Giles and Jeff Bagwell stunk up the joint for me in K15 the first 60 games last year. But they got hot over the last 100 games and as a result so did the rest of my team.

Their batting averages were low but their OPS (OBP + SLG) was within reasonable bounds for the season as a whole (of course it was a little on the low side due to the early slump -- but it was reasonable).