Ok, your driller is a moron first and foremost. Thumb is supposed to go in as deep as it can point blank and period. There is no way you can put it in too deep, that's bull. Thumb is going to tell you when to stop. Your span is now too long forcing you to grab it and, depending on you pitches, aslo forcing you to hold on to it. If you span is too long and your pitches are reversed you will have no choice but to grab it because the ball wants to come off quick. Where ever you go to get your balls drilled, dont go back! I just hate to see guys do this, unnecessarily make drastic changes.
That being said, here's how you fix it. You can do this at home. Take a ball put your thumb in it, AS DEEP AS IT'LL GO! Set your palm flat on the ball. Mark where your thumb is in the ball. Then mark your fingers, splitting the distance between the 1st and 2nd joint. Put you thumb back in the ball and, with a grease pencil, mark the ball where the marks on the fingers are. THATS YOUR SPAN! Now put your hand in the ball fingers first and i almost guarantee the line on your thumb will be higher. Just for giggles, mark it in ball again and measure the distance between the two marks on your thumb.
Guys, for some reason want to lengthen span because they are too lazy to do the math and the work to fix a problem with pitches or they dont know how to do the math. Sorry, if this is the case, that you had to deal with bad ball fitting from someone who wasnt smart enough to do his job.