gwnn, on 2011-August-06, 09:53, said:
Frances, what I would be afraid of is a distributional hand with 5 spades, say 10 points and a singleton, where I would be happy to give game a shot if I knew partner had 3 card support, even if they're 12-13, but I'd like to play in 2♠ if they have only 2 spades. If my partner merely tells me that they have 12-13, I will be forced to bid 2♠ and we will miss some nice games. This seems to be a problem regardless of the zone you put in the 2♦ rebid, and of course best is to give us most room for a parking space when partner is weakest (4153 like you said), but I would be a little scared.
So why not use the 2♦ and 2♥ responses to the checkback as both weak?
(Assuming 5 card majors, natural spade response, 1NT rebid = 12-16 denying 6 hearts)
2♦ = 12/13 without 3 spades
2♥ = 12/13 with 3 spades
2♠ = 14/15 with 3 spades
2NT = 14/15 without 3 spades
3 any = 16 and a 3 card fragment