  Flow-like signals including the ridge structure observed in small collision
systems that are similar to those in large collision systems have led to
questions about the onset of collectivity in nuclear collisions. In this study,
we use the string melting version of a multi-phase transport (AMPT) model with
or without the sub-nucleon geometry for the proton to study multiparticle
cumulants in $p+p$ collisions at 13 TeV. Both versions of the model produce
negative $c_{2}\{4 \}$ values at high multiplicities. In addition, the
dependence of $c_{2}\{4 \}$ on the parton cross section is non-monotonous,
where only a range of parton cross section values leads to negative $c_{2} \{4
\}$. Furthermore, the AMPT model with sub-nucleon geometry better describes the
multiplicity dependence of $c_{2} \{4 \}$, demonstrating the importance of
incorporating the sub-nucleon geometry in studies of small collision systems.
