It looked to me that the 3's Hield hit were due to defensive errors by our defender - hesitating in rotating or closing out - and not holes in the defensive plan. I think the double-team plan did a good job keeping us out of foul trouble, helping us dominate the points in the paint, and causing OU to take a lot of difficult shots, many of which were quick jump shots. The weakness was that it put us out of position to rebound those quick jump shots, which also tend to lead to a high number of long rebounds (often 50/50 balls).
The summary at the end shows an OU team that shot a poor percentage (40.6%), lost the turnover battle (-4), lost the Points in the Paint (-12), and won on the boards (+12) against ISU. I think the double-team the post plan worked very well when looking at the big picture.
The game was closer than it could have been (which I assume to be the root of this thread) due to ISU only grabbing 6 offensive rebounds, having a few periods where we stopped moving the ball in the half court and forced things 1 on 1, and OU hitting a fair amount of difficult shots, IMO.