1) with such as
KJxx
KQTx
xx
xxx
I'd like to be able to open 1H for lead (without P driving me on to game/doubling aggressively if the opps get involved).
2) with such as
QJxx
KQ
Jxxx
KJxx
I'd like to be able to open, but don't want to bid a weak NT and have P raise me to 2, or get doubled (esp vul) by a powerful hand on my left.
3) with such as
KQxxx
Qxx
Axxx
x
I'd like to be able to open at the one level and find our best fit when the part score is ours.
So I spent a while trying to modify the system for third and fourth seat openings. With what I've come up with, you'd still do better out of such hands playing a normal system (esp on hand type 3, which I haven't really satisfied myself about), but I've at least been able to give a few options:
1♣ is still full strength (in fact stronger, since the 1N range has changed. If balanced, it's now 17+)
1♦♥♠ can now all be arbitrarily weak, so long as you have enough tolerance to pass any natural call P might make.
1N is now 14-16 bal.
2-bids are unchanged (ie very wide ranging in 3rd)
P of course assumes in competition that you have a weak hand.
In constructive auctions, these bids are still F1.
If P responds at the one level (inc 1N), raises your suit or bids 2♣ over 1♦ or 2♥ over 1♠, any call other than pass promises a full strength Fantunes 1-bid, and system is still on.
***
After a 1M opening, we have two Druryesque bids:
2♣ shows 10-11 points with 2 cards in your suit*
2♦ shows 9-11 points with 3 or more cards in your suit
* The key here is that with a singleton and this point range, P would normally have opened a Fantunes 2-bid. With a misfitting 4441 and 10-11, he has to content himself with a semi-forcing 1N response.
***
After 1M 2♣, opener's 2 of a new suit is to play (inc after a reverse!), and responder should almost always pass. With 4♣ and a min balanced, opener will pass. This guarantees a 4-3 or better fit unless responder is exactly 5422 with doubletons in both opener's suits.
After 1M 2♦, bidding can be fairly natural, obv with 2M as a hard sign-off, though you might have 2N as a forcing enquiry since opener is still unlimited and responder has a narrow range of hands.
***
Anything else is fairly flexible. For eg, after 1♠ 2♥ / should opener's 2♠ rebid be GF? I actually ended up thinking it should be NF inv (opener would have opened 2♠ with a weak hand, is guaranteed 2-card support, and can force with various higher bids if he so chooses).
So on the hands above
1) can open 1H, planning to pass 1♠ or 1N, pull 2♣ to 2♠(!), or 2♦ to 2♥.
2) can choose:
a 1♦ opening, planning to pass any response
Possibly your answer would depend on the form of scoring.
3) doesn't really have its problems solved - with this shape it could open 1♠ planning to pull 2♣ to 2♦, but that might land you in a 4-3 rather than a 5-2, and possibly worse, you'd have to pass p's 1N. I would probably still just open it 2♠.