short bpfsl compared to much bigger bpel?

Hi guys

If a guy has a much shorter bpfsl compared to their bpel does this mean they don't have a very tough tunica?

I ask this because after a lengthy warm up my bpfsl is 4.5 inches where my bpel is 6 inches. So it grows 1.5 inches bigger than it's bpfsl, so my naive understanding of this is, because many guys erect penis doesn't grow bigger than their bpfsl because their tough tunica doesn't let it, where my penis can grow a further 1.5 inches bigger than it's bpfsl, so this would mean my tunica isn't tough? So is my assumption right or wrong?