The flavour structure of hypothetical new physics at the TeV scale is constrained by many observables across different energy scales, ranging from low-energy flavour experiments to high-$p_T$ observables at the LHC. We discuss how, for example, Drell-Yan tails can provide a good complementary probe of flavour in the SMEFT. An interesting pattern emerging from the data is the possibility of having new physics coupled mainly to the third generation of fermions. We show that in this case the limits on the effective scale can be lowered down to the TeV scale, using the SMEFT in the $U(2)$-symmetric limit. This particular structure can be obtained in so-called 4321 models, featuring quark-lepton unification in the third family. Within this class of models, we discuss some interesting effects in $\tau$ decays and electroweak precision tests.