  The efficiency of the $\gamma$/hadron separation worsens significantly at low
energies for Imaging Air Cherenkov Telescopes (IACT). This observed effect was
partially explained by the occurrence of a hardly reducible hadronic background
(i.e. detected images that are formed mainly by the light from a single
electromagnetic or a single $\pi^0$ sub-cascade in the proton induced shower)
[1,2]. IACTs also record events containing Cherenkov light from at most two
electromagnetic sub-cascades, which don't have to be products of single $\pi^0$
decay in the hadron initiated showers. In this paper, the impact of at most two
electromagnetic sub-cascades events on the primary $\gamma$-ray selection was
studied using the Monte Carlo simulations. We investigate how the total
fraction of at most two sub-cascades events in the expected total protonic
background depends on the hadron interaction models (GHEISHA and FLUKA),
trigger threshold, reflector area and altitude of the observatory. We show that
the efficiency of the $\gamma$/hadron separation is anti-correlated with the
contribution of at most two electromagnetic sub-cascades events in the proton
initiated showers below 200 GeV. The influence of at most two electromagnetic
sub-cascades events on the $\gamma$-ray selection is similar to the effect of
the single electromagnetic sub-cascade and singe $\pi^0$ events in IACT
observations. The occurrence of all these images in the data collected by IACTs
reduces the efficiency of the $\gamma$/hadron separation at low energies.
