It is well known that the proper pairing for a crested bird is a non-crested bird. And that we must avoid breeding two birds with the same fault and rather chose birds that complement each other.
But what would you expect to happen to the beautiful desired rounded crest if you breed it to a mate that looks like the non-crest standard? Breeding a non-crested bird shaped like the standard, will encourage an oval instead of round crested offspring.
To produce the desired rounded crest, the non-crested mate must be more rounded shape than the non-crest standard. I have shaded in the desired roundness that will produces offspring with more rounded crest.
The desired roundness of the non-crested bird includes the entire head and neck. Even the roundness of the back-skull is important to ensure the crest blends in, without any breaks in the back of the neck.