Glad you mentioned that it is not a great idea to breed to the sire but rather the grand sire.
I agree that we must be methodical when we start constricting the gene pool in the F2 and F3 progeny.
a true F2 progeny ( F1 X f1 from a same pairing ) is the great genetic expression of the parent stock .wide variation is expected if the parent stock where from different origin
must be done to uncover the true genetic make up of the breeders.
if we cross strait back to the sire we are reinforcing not only the quality but the Fault too.
crossing back to the grand sire will give us a time to clear the fault in the F1 and F2 progeny before crossing back and reinforcing just a quality ( because by now it is a dominant trait after 2 generation )
chooks man