I have an interesting hand that I'd like you to look at. I think your formula overvalues it. The hand is from The Complete Book on Balancing by Mike Lawrence, page 199, 4th hand. I will relist it here:
|K J 7|
|A 10 7 6 4 2|
|A 6 5 2|
|Q 9 8 6 5|
|7 5 4 2|
I think your formula would suggest bidding 4. WP = 6+7+7 = 20. In fact it may be higher because the heart suit may drop an honor, or even 2.
SST = 0+2 = 2, with -1 for the 2nd Doubleton = 1. 13-1 = 12 tricks, 20 WP = no adjustment.
I think the reason it overvalues the hand is that the clubs must be ruffed with high trumps. This is a case where having a 9th trump is extremely valuable.
The solution is to use judgment, and not just plug and chug a formula. The North player should realize he will have to ruff Clubs with high trumps, thus incurring additional trump losers. Therefore he should downgrade his hand.
I find the formula helps me tie together what I've read in the 3 books 'The Complete book on' Hand Evaluation, Overcalls, and Balancing. It helps me try and visualize the distributions in the 4 hands, rather than just use a generic formula.
As we have written elsewhere, our formula predicts how many tricks one side can take if nothing bad happens. And, indeed, if we only look at North-South's cards, they have the potential for ten or more tricks: on a non-club lead, hearts may be ruffed out, giving South four trumps, five hearts and two diamonds (11 tricks); and on a club lead, South can ruff three clubs in dummy to go with four red-suit tricks and three trump tricks in his own hand (10 tricks).
But if we view the situation from North, he knows his long side-suit won't produce lots of tricks after East's 1 opening bid. Furthermore, North doesn't have lots of trumps to ruff with. Therefore, he should downgrade his hands, just as you say. If you click on What's important->Errors in the left frame, you'll find a discussion on this very topic under the heading (2) Not enough potential. The deal above fits into this category (very low SST, not lots of trumps, no trick-taking side-suit).
It is also true that a fourth spade would be useful. And if North has 4-6-3-0 instead, the potential goes up so that the formula predicts accurately. On normal breaks, you can expect four trump tricks in hand, one or two club ruffs in dummy, five hearts and ace-king of diamonds. Once again, a bad split in trumps or hearts may mean North-South lose one (or two) of those tricks, but that doesn't mean the prediction is wrong.
Conversely, if North's distribution is 3-4-6-0, he can expect his long side-suit to be much more useful than when East has bid it. West's club bid also means that South isn't likely to have lots of wasted values opposite the void. Taking a shot at 4 in that scenario looks good to us.
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