Everyone I know plays a good defense to an opening 1NT. Most of them have discussed dozens of variations and all the follow up auctions. Yet how many of those people use an artificial defense to a 1NT overcall? Most people make good with, «Double shows a strong hand and everything else is natural and non-forcing.»
Can we improve on that approach? Yes!
When the opponents overcall a strong NT, our bidding focus is competing for the partscore. We won’t hold game values often and when we do we will either double for penalty or we will jump to game based on some freakish distribution.
When competing for the partscore, our priority is major suits. When our fit is in a minor, we are doomed to lose most of the auctions since the opponents can outbid us at the same level in a major. However, when we hold a major fit, especially a spade fit, the hand could belong to us and missing that fit could cost us a double partscore swing.