You guys, plus some patience, perseverance and a few choice words on my part, finally paid off.
My goal was a .965-.968 league fielding average and 1200-1250 league double plays.
I don't know if this was the key, but I turned off "automatically league strategy when advancing to the next season" on the Game Settings screen.
I did this in the "preseason" and made sure my changes were still in the game on opening day... THEY WERE!
Set the Position Modifiers to 2.000... pretty much doubling them over the game settings.
Set Double Play Grounder to 1.111
Set Double Play Line Drive to 2.222... increased both of them by about 20% over the AI settings.
Got what I wanted... League Fielding Average .968 and 1275 double plays.
Boy, it's been a good day!