Novel functionalities may be achieved in oxide electronics by appropriate stacking of planar oxide layers of different metallic species, MO p and M'O q . The simplest mechanism allowing the tailoring of the electronic states and physical properties of such heterostructures is of electrostatic nature-charge imbalance between the M and M' cations. Here we clarify the effect of interlayer electrostatics on the anisotropic Kitaev exchange in H3LiIr2O6, a recently proposed realization of the Kitaev spin liquid. By quantum chemical calculations, we show that the precise position of H+ cations between magnetically active [LiIr2O6]3- honeycomb-like layers has a strong impact on the magnitude of Kitaev interactions. In particular, it is found that stacking with straight interlayer O-H-O links is detrimental to in-plane Kitaev exchange since coordination by a single H-ion of the O ligand implies an axial Coulomb potential at the O site and unfavorable polarization of the O 2p orbitals mediating the Ir-Ir interactions. Our results therefore provide valuable guidelines for the rational design of Kitaev quantum magnets, indicating unprecedented Kitaev interactions of ≈40 meV if the linear interlayer linkage is removed.