Probing the transverse size of initial inhomogeneities with flow observables

Disentangling the effect of initial conditions and medium properties is an open question in the field of relativistic heavy-ion collisions. We argue that, while one can study the impact of initial inhomogeneities by varying their size, it is important to maintain the global properties fixed. We present a method to do this. We show that many observables are insensitive to the the hot spot sizes, including integrated v_n, scaled distributions of v_n, symmetric cumulants, event-plane correlations, and differential v_n(p_T). We find however that the factorization breaking ratio r_n and sub-leading component in a Principal Component Analysis are more sensitive to the initial granularity and can be used to probe short-scale features of the initial density.