Semi-major axis a (line), the heliocentric distance r (dots) versus time t (bottom panel), and the embryo mass M_em versus t (top panel) for the nominal simulation with initially four embryos. The time span 4000 P_orb correspondsto 47.4 kyr. Although it was already presented in Chrenko et al. (2017), we show it here to provide an easy (1:1) comparison. The grey strips indicate the inner and outer damping regions used to gradually suppress spurious reflections. The black arrows indicate two interesting events we study in detail: a merger (3+4), and a co-orbital formation. The semi-major axis may exhibit a “spike” during a close encounter, but in fact r ≪ a; the body is far from the damping zone.