Currently I'm flying a PA-28 181 for my boss and he insists on leaning the mixture all the time. Problem is he just pulls the mixture back to where ever he feels like and he does this at any altitude. I thought you leaned above 3000ft? He does this all the time when we are shooting approaches where we are at 2100-2400 ft msl, then going missed and adding full power still leaving the mixture leaned. Can someone chime in with some advice, because this is not how I learned how to lean. Thanks