Expanding on what Vlad said...
You still won't be off more than the distance between the top of your front sight and the bore-axis with the irons zeroed that way. The closer you get to the target (from 25), it would be physically impossible for you to be "4-6"+" off, as you say, because there simply isn't enough elevation in the sights to make a difference. Check out the graphs in this
thread to give you a better idea. You'll notice that none of the zeros, whether 25, 50 or 100 yards cause the round to ever go 'lower' than the distance between the front sight post and bore-axis before ~25 yards.
Bottom line: Zeroing irons as FTS suggests won't make a difference for your CQB hold-offs.