Bigfoot 2500 series on a short box

one of the" real world " problems that MAY? cause u problems is the locations of the bump outs on the Bigfoot basement tub in relation to the trucks wheel well tub ? note a BF 9.4 sb has a overall floor length of 16-6 ,a Bf 9.4 lb has the same and so does a 9.6
SO why will one work but not the others ?????? they all use the same base tub length !!!!!!!! And years of my research has revealed no discernable difference to explain the reasoning for different classifications ?????????????