The general "rule" for my style of cuebidding is that a cuebid in a suit that the cuebidder initiated shows two of the top three honors.
So, for example, after 1S-P-2C-P-2D-P-2S, Opener only cues 3D if he has two of the top three honors in diamonds.
However, note that the failure to cuebid 2NT (a trump quality denial cue) means that Opener also has two of the top three honors in trumps, the latter known by inference.
So, let's cramp up the auction a bit. 1S-P-2D-P-3C-P-3S. A very similar auction, with one major difference -- we have lost a round of cuebidding. That major difference deprives us of both a 3S cue as a trump cue and the 2NT cue as a denial cue.
In this situation, there might be some merit to consider expanding the thought process for a 4C cue. Normally, a 4C cue shows two of the top three honors, in clubs. Also, this is a courtesy cue (Opener did not cue 3NT to show serious interest).
Well, it seems somehow strange to me, in thinking this through, to have a mmeans for Opener to define his external strength (his strength in clubs) but not his internal strength (his strength in trumps). In other words, it seems odd that a 4C cuebid cannot be made unless Opener has at least KQ, but Opener could have just about anything in trumps.
I have not thought through the permutations of an alternative approach, but it seems to me that it would be workable for Opener's cramped-space cuebid of a side suit to not show two of the top three honors in clubs but to rather show what could be called "internal strength."
"Internal strength" is a concept that looks both at clubs and at trumps. In this situation, clubs and spades.
"Internal strength" could be defined in several ways.
It could mean one of two holdings: (A) two of the top three clubs, or (B) one of the top two clubs and two of the top three spades. With this definition, Opener could cue 4C with AQ, AK, or KQ in clubs, even if he has no spade honor. Or, Opener could cue 4C with just the sole Ace or King of clubs, so long as he has two of the top three spades.
The problem with this definition is that the net honor contribution is variable. Another alternative might be more pure. For the "pure three" method, a 4C call could be made with either (A) two of the top three clubs and at least one of the top three trumps, or (B) one of the top two clubs and two of the top three trumps.
Suppose that Responder is looking at two of the top three trumps. If he hears a 4C call from Opener, Responder would know that Opener has two of the top three clubs. If, however, Responder is looking at two of the top three clubs, then he would know that Opener has two of the top three trumps, and the missing club honor. Thus, when Responder has two of the top three cards in one of Opener's suits, the meaning of opener's courtesy cue would be clear.
However, what if Responder only has one of the top three cards in each black suit? In that event, Responder would know that either clubs are solid or trumps are solid. Either one might be enough. However, there is a serious problem that you may spot. What if Responder has all three top spades?
Well, then maybe a third option for "internal strength" emerges. (A) Two of the top three clubs plus one trump honor, or (B) one of the top two clubs plus two trump honors, or (C) all three top club honors.
Either of the second or third options will limit Opener's opportunities to cue 4C, but they would each be more descriptive. The first option would allow the cue to be made more often, but then this would cost in description reliability.
I suppose a fourth option comes to mind, a variation on the first. (A) Two of the top three clubs, or (B) two of the top three trumps and the club Ace.
Any thoughts on this?