You over complicated it.
The "Daddy"/"Hidden"/"sib" gene is just another allele in the BluEL complex. A Platty is basically a really dirty BluEL. It is a combo of Lesser and "Daddy"/"Hidden"/"sib" in the same manner that the MysticPotion is a really dirty BluEL combo of Mystic and Mojave.
A Platty bred to a normal gives you Lessers and what RDR calls "sibs". These "sibs" carry the "Daddy"/"Hidden"/"sib" gene, none of the Lessers carry the gene or they would be Platty. Breeding a "sib" back to any other het BluEL has the potential to give rise to a "Daddy"-type combination that is dependent on what the non-"sib" parent is. That is why RDR got ButterDaddy when he bred a Butter to a "sib" and Phantom44 (RDR's name for the Phantom/"Daddy" combo) when he bred a Phantom to a "sib". Neither the Butter parent nor the Phantom parent in those crosses had any relation to the PlattyDaddy so the "Daddy"/"Hidden"/"sib" allele came only from the "sib" parent.