When Johan Bennet (European Pairs Champion, Cavendish winner, Bermuda Bowl bronze) was doing his deep thinking about leads and doing simulations, almost 15 years ago, he came up with another one I've practised faithfully ever since. And this has been a big winner over the years. Trust me.
It concerns what lead strategy you should adopt after (1NT) all pass. He purposed this algorithm:
a) With a 5-card suit, lead it.
b) With 4333, lead the 4-card suit.
c) With 4432, lead the weaker 4-card suit.
Where the break-off point is concerning c) when the suits get closer to each other in quality hasn't been discerned. Some things are too tough to call.
I'm not breaking down the details, but higly recommend this approach. An important side-effect is that it also makes it easier for partner when making decisions later in the deal if you know this algorithm is followed. After 1NT-opening, not much information is disclosed on suits lengths.
The secret is out.