  Context. The scale height of the spatial distribution of open clusters (OCs)
in the Milky Way exhibits a well known increase with age which is usually
interpreted as evidence for dynamical heating of the disc or of the disc having
been thicker in the past.
  Aims. We address the increase of the scale height with age of the OC
population from a different angle. We propose that the apparent thickening of
the disc can be largely explained as a consequence of a stronger disruption of
OCs near the Galactic plane by disc phenomena, namely encounters with giant
molecular clouds (GMCs).
  Methods. We present a computational model that forms OCs with different
initial masses and follows their orbits while subjecting them to different
disruption mechanisms. To setup the model and infer its parameters, we use and
analyse a Gaia-based OC catalogue (Dias et al. 2021). We investigate both the
spatial and age distributions of the OC population and discuss the completeness
of the sample. The simulation results are then compared to the observations.
  Results. Consistent with previous studies, the observations reveal that the
SH of the spatial distribution of OCs increases with age. We find that it is
very likely that the OC sample is incomplete even for the solar neighbourhood.
The model simulations successfully reproduce the SH increase with age and the
total number of OCs that survive with age up to 1 Gyr. For older OCs, the
predicted SH from the model starts deviating from the observations, although
remaining within the uncertainties of the observations. This can be related
with effects of incompleteness and/or simplifications in the model.
  Conclusions. A selective disruption of OCs near the galactic plane through
GMC encounters is able to explain the SH evolution of the OC population.
