- I believe that, as far as possible, balanced hands should show their strength with their opening bid (see DavidC's bridge blog). It seems many top players agree with this, as a fair few are using 2m openings to show 18-19 balanced in the Europeans.
- The ranges used in 3rd+4th should depend on those used in 1st+2nd. Basically, your lowest range should rule out bidding to game unless you have a fit, which IMO should mean that 24 points between the two hands is possible, but 25 is not. In practice, this means that, in either 1st+2nd or 3rd+4th, your lowest range will be 11-13, and your next range will be 14-16.
These two points conflict greatly. While I don't too much mind opening a natural 1m on 18-19 balanced, doing so on a balanced 17-count is undesirable, to say the least - 17-counts are a fair bit more frequent than 19-counts, and more dangerous to take another call on. Likewise, opening 2m with 17-18 or 17-19 seems to be taking a reasonable idea too far.
So, to solve this, we need a "tri-bal" system - one which allows us to show three balanced ranges immediately at the one-level.
The most obvious solution is strong club - 1♣ shows 17+, 1♦ includes 11-13 balanced, with a 14-16 1NT opening. The problem with these systems is that they give you problems on the club hands - especially when holding 4M5♣ and 14-16 or so (the 11-13 4M5♣ hands can get away with opening 1M IMO, but the 14-16s cannot - see more from DavidC). Likewise, strong diamond gives you the same problem on diamond hands.
I've posted one attempt at solving these problems already, and here is another one that I haven't really evaluated yet -
1C 17+, not 4M5+m
1D 11-13 bal/14+unbal 4M5+m
1M can be 4 if 10-13
1N 14-16
2m 11-16 no 4M
It might be better to put the 14-16 minor single-suiters into 1D, and make the 2m openings 9-13 - preemptive and constructive like Fantunes, but without the worry of opener having a four-card major on the side.
These structures bring me to a third point. It's advantageous to separate balanced minimums from unbalanced minimums, as in Polish Club, Swedish Club and the structures above. This is because you can then treat the opening as a weak no-trump; negative freebids become much easier to handle and useful when partner has a stronger hand too.
And, just to eliminate one possibility, something like 1♣ any 14-16 and 1♦ any 17+, with an 11-13 NT isn't an option - firstly because I don't think a weak NT is playable in 3rd seat, and secondly because it wouldn't be legal in the EBU - an artificial 1m opening cannot include unbalanced hands with 5+M and fewer than 16 points (unless it is a transfer opening, of course).
Hopefully I'll find something that satisfies all my aims

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