We derive the modified QS mapping for disformal coupling and show that the effective boost becomes (1+f)/(1+h), breaking the additive structure responsible for the slope obstruction in Paper XIII. The disformal denominator provides an independent slope correction not constrained by the conformal suppression factor f/(1+f). This is a structural result establishing that the XIII obstruction is specific to conformal coupling, not generic to scalar-tensor theories.
Arturo Cerezo (Mon,) studied this question.