My weak NT experience says that, if holding a balanced hand, opener almost always has stoppers (since opener is 15+). So my structure over 1m-2m is simple and ignores stoppers:
new suit = natural unbalanced
2N = 17+ balanced
3N = 15-16 balanced
jump in new suit = splinters, including extras
But we don't bid 1m-2m with a 4 card major, and this structure would lose 4-4 fits if opener is balanced and responder has a 4 card major. I don't really see a good way out - I suppose you could use 1m-2m-3M to show 15-16 balanced with a 4 card major, but you lose the splinters which are actually quite useful.
This is exactly one of the prototypical hands to bid 3M after 1m-1M, playing weak NT - 17-19 (semi)-balanced (or 15-17 unbalanced). Yes knowing the double fit is good, but it's not a big deal if you don't have tools like 6 keycard BW.
North should bid 5D after keycard to look for the QH and KD and the grand. South cannot have 0 keys after the 3H raise.
mikeh, on 2023-January-20, 22:06, said:
I’ve never seen what I would consider to be a good structure for handling inverted minors where responder could have a four card major.
The problem is that there are a lot of things the partnership needs to explore other than looking for a 4-4 fit in a side suit.
Traditionally opener showed stoppers rather than length. So 1D 2D 2H would (usually) just show a heart stopper and at least no stopper in one of the black suits (else 2N)
More sophisticated methods identify whether opener’s hand is balanced, shapely, minimum, maximum or in-between.
Once you start using 1m 2m 2M as simply ‘I have a four card major’, one can’t help but lose a great deal of bidding space on the other, mor common hands where no 4=4 major fit exists.
In addition, if you play that 1D could be three, then responder doesn’t really know that they have a double fit. If you play it is always 4 then, unless playing 4 card majors, your 1C is 2+ and now 1C 2C really doesn’t mean a double fit exists…clubs may be opener’s shortest suit!
Which would be ok, I suppose, except that the sequences that begin 1m 1M are really straightforward. I note, btw, that you explain the 1D 1H 3H as showing 15-17. Two points: the hand has 18 hcp so responder bought a surprising dummy. Secondly, if playing strong notrumps, 3H shows an unbalanced hand, else why not 1N? But I think you play some weak notrump?
My own thinking is that it’s not worth screwing up an inverted method since, imo, the 1D 1M approach is either already well developed or could be with some work.
You wrote that you adopted this form of inverted minor because of fears of screwing up 1m 1M auctions. Maybe you could elaborate on that, since right now I think you’ve adopted a solution that creates more problems than the problems you’re trying to avoid.