While I agree with what you say, there was one time I thought it was a positive that the umpire showed a little bias. DD was pitching and everytime the umpire would call a ball that she thought was a strike she would roll her eyes and/or shake her head. After the second batter the umpire called the coach over and basically said "I'm not going to be shown up by a 10 year old, she does it again and she's out of here". Coach relayed message to DD. Next pitch was down the middle. "BALL", DD didn't even flinch. After that he went back to calling a pretty good game. Best miscall ever for DD. She now knows that she isn't in charge and waits until well out of sight/hearing of Blue to whine. And yes, I did find Blue after game and thank him.
IMO I think using a different approach may come across better. Such as, "Blue, I'm trying to help my girls adjust, is she hitting the front corner?" Then you aren't questioning his calls, but at the same time you bring awareness to the possible situation going on if the pitcher isn't hitting any part of the plate.
Human nature does come into play here. I coach and have umpired
plenty of games. The coach who constantly whines to Blue during changeover
gets less and less calls. We all know how good pitches look from the bucket
in the opening of the dugout
When I sit on a bucket 15 to 20 feet away from home plate, I first watch where a catcher sets up and where she sets up the target. With an 0-2 or 1-2 pitch, a smart catcher sits up outside and puts the target 1-2 feet off the plate hoping the pitcher hits the target and the batter swings.