  We analyse the possibility of describing quark masses, mixing and CP
violation in $S'_4$ modular flavour models without flavons. We focus on the
case where the closeness of the modulus to the point of residual
$\mathbb{Z}^{ST}_3$ symmetry (the cusp) plays a role in generating quark mass
hierarchies and discuss the role modular form normalisations play in such
constructions. We find that fitting quark data requires explicit CP breaking,
unless a second modulus is introduced.
