Regarding reducing W-4 withholding, your employer probably won't ask why your deductions are higher than it seems they should be, but if they do, you can't tell them why, because once they know the information on your W-4 is false they're not legally allowed to accept it.
Be prepared to give them an innocuous answer, such as, "I am confident that I've filled out my W-4 correctly," or, "The information I've put on my W-4 is consistent with my private financial circumstances." (4/11)