Bogusevic, who entered Wednesday's game hitting .189, was ranked 15th in the National League in terms of the percentage of pitches he has taken this year. He drew a walk on a full count in his first at-bat against Milwaukee's Shaun Marcum on Wednesday.
Bogusevic has been hitting a lot of ground balls right at defenders after falling behind in the count instead of driving the ball the way he did last year.
"I might be completely wrong here, but a lot of it comes with not being real aggressive, to where he's getting behind in the count and tries to make contact instead of being able to stay aggressive and let it fly," Mills said. "So what happens when you make contact? It's a little ground ball."
Bogusevic, who has started 15 of 19 games in right field, was hitting .267 with two triples and five RBIs in his nine games prior to Wednesday.