  Inside-Out Planet Formation (IOPF) is a theory addressing the origin of
Systems of Tightly-Packed Inner Planets (STIPs) via {\it in situ} formation and
growth of the planets. It predicts that a pebble ring is established at the
pressure maximum associated with the dead zone inner boundary (DZIB) with an
inner disk magnetorotational instability (MRI)-active region. Using direct
$N$-body simulations, we study the collisional evolution of planetesimals
formed from such a pebble ring, in particular examining whether a single
dominant planet emerges. We consider a variety of models, including some in
which the planetesimals are continuing to grow via pebble accretion. We find
that the planetesimal ring undergoes oligarchic evolution, and typically turns
into 2 or 3 surviving oligarchs on nearly coplanar and circular orbits,
independent of the explored initial conditions or form of pebble accretion. The
most massive oligarchs typically consist of about $70\%$ of the total mass,
with the building-up process typically finishing within $\sim 10^5$ years.
However, a relatively massive secondary planet always remains with
$\sim30-65\%$ of the mass of the primary. Such secondary planets have
properties that are inconsistent with the observed properties of the innermost
pairs of planets in STIPs. Thus, for IOPF to be a viable theory for STIP
formation, it needs to be shown how oligarchic growth of a relatively massive
secondary from the initial pebble ring can be avoided. We discuss some
potential additional physical processes that should be included in the modeling
and explored as next steps.
