A Marans breeder friend of mine that shows her birds told me it only takes one good rooster to turn it all around. In order to get that one good rooster, you have to look closely at your hens and breed only the best hens you have. Chooks man is right, we have to give hens their due credit because they are a heavy influence on the birds we produce.
While type and size of the males comes greatly from the hen, tail angle most definitely is passed from both the sire and the dam to the offspring. I have proof in my cull pen unfortunately. All of my cockerels from Apollo and Sheraz inherited his high tail. Chooks man has explained what traits come from which parent, and everything he has told us is proving true.
In order to breed birds with longer backs and lower tails, you must select your breeders that have the longest backs and lowest tails. If your rooster has a short back and high tail, mating him to a long backed, good tailed hen will help throw some birds that are an improvement over their sire but not all of them. You will still have lots of culls. You may not get everything right in one generation, but you will see some improvement if you breed this way. Even though my Apollo has a short back and a high tail, all of his sons and daughters have their mother's longer back, so that is an improvement. We have to look closer at our hens like Redbanks mentioned because the rooster is only half of the equation. My husband tells me all the time that a good rooster comes from a good hen, and that is so very true.
Single mating, selective breeding, hard culling, and balance in the breeding pen are the keys to producing better quality birds.