Have you ever wondered why there are so many
conventions for competing when an opponent opens a strong 1NT? Here is
a short list: Brozel, Pinpoint Astro, Ripstra, DONT, Hello, Landy,
Lionel, and Cappelletti. Currently DONT is favored by experts playing
2/1, Cappelletti by SAYC club players, Landy in Europe and Lionel in
Australia-New Zealand. The proliferation of conventions in this one
area is a sign that no one of them is entirely satisfactory.
If we look more deeply into the matter of competing against strong no trump opens we discover that there is a fundamental difference between what we would like to be able to do (and avoid doing) in the direct seat (LHO opens 1NT) vs what we would like to be able to do in the balancing seat (RHO has passed opener’s 1NT). The various conventions are all compromises because they are applied in both seats indiscriminately. In effect we have a choice of various “all purpose” tools, none being totally satisfactory, when what we really want are two different tools, each specialised for its particular seat.
In the direct seat we want to be able, with a biddable suit and keeping an eye on the vulnerability, to be able to make overcalls at the two-level as often as possible in order to disrupt our opponents' Stayman and transfer sequences. Because single-suited hands occur about three times as often as two-suiters,1 the most effective defense in the direct seat will, therefore, allow for immediate natural overcalls in diamonds, hearts and spades. In addition to this interference, we'd like to be able to compete for a part-score whenever we do get a two-suiter with some values.
Now, come around to the balancing seat. Here, there is no hurry at all in getting in a two-level overcall to interrupt opponents' communications since they have abandoned the auction at 1NT. With the responder (your RHO) passing, the balance of power must be about equal, so we certainly do want to be able to compete in this auction any time we have a couple of distribution points (two doubletons or a singleton), regardless of how many high card points we have.2