[apollo1201]

IMPs, green against red, after 2 passes you have the nice following collection that you open 1C (strong NT, 5cM context):

QTx
Axx
x
AKQJxx

LHO bids 3D and partner Xes, for majors.

RHO passes but now what. 3NT hoping for a blockage or a stopper in partner’s hand given the pass of RHO (but they are red, and after seeing their partner pass, LHO could have a bit more strength but 6-cd only)? 4D hoping partner has a 5-cd M (she will often be 54 but not necessarily)? 5C?

Actually partner was 6412 so we lost 2 IMPs after my lousy 5C bid when they made the same 11 tricks in 4S.

RHO had passed with Axxx D and a side goodie but had they bid, it would have been easier (X).

[DavidKok]

I would bid 4♦. Partner might have 5-4 in the majors, as you say, and even with less shape the 4-3 Moysian fit might be the best contract. It helps that either way the diamond shortness will be in the hand with the fewer trumps, which creates extra tricks.