Would the body shape come more from the male or female? In other words, in an ideal world, you would choose your widest back end birds of each sex and breed them, continuing to select for wideness in the back end and then hopefully fix the shape. But, if you didn't have wideness in both sexes, would one or the other parents be more likely to pass on its body type? I guess what I'm asking is if I was trying to correct this problem, would it be better to go out and purchase a good bodied cockerel or a good bodied hen?
I would call it breeding extremes, or putting pieces together. I would breed birds with narrow tails to birds with "extreme" or overblown tails, regardless of sex. Kind of back to the "breeder bird", "show bird" discussion. Just suggested the Darks because maybe gold partridge with the wide rear-ends may not exist....I really don't know.
Tim