Yes, with Ameraucanas, bigger is not necessarily better. The muffs and beards can be too full and fluffy, like Faverolles, and that would not be correct type. The byword for Ameraucanas is medium.
Actually, in a cross of homozygous for muffs and heterozygous for muffs, half of the chicks should be homo and the other half hetero. The expected ratio can be demonstrated with a Punnett square diagram. Or think of it this way. All the chicks will receive a muff gene from the homo parent. Half the chicks will receive a muff gene from the hetero parent, and the other half won\'t.