  The high-quality structures containing semiconducting transition metal
dichalcogenides (S-TMDs) monolayer (MLs) required for optical and electrical
studies are achieved by their encapsulation in hexagonal BN (hBN) flakes. To
examine the effect of hBN thickness in these systems, we consider a model with
an S-TMD ML placed between a semi-infinite in the out-of-plane direction
substrate and complex top cover layers: a layer of finite thickness, adjacent
to the ML, and a semi-infinite in the out-of-plane direction top part. We
obtain the expression for the Coulomb potential for such a structure. Using
this result, we demonstrate that the energies of excitonic $s$ states in the
structure with WSe$_2$ ML change significantly for the top hBN with thickness
less than 30 layers for different substrate cases, such as hBN and SiO$_2$. For
the larger thickness of the top hBN flake, the binding energies of the excitons
are saturated to their values of the bulk hBN limit.
