An experiment for measuring the flux of gamma rays of cosmic origin with energy above 100 TeV (the Carpet-3 experiment) is currently being prepared at the Baksan Neutrino Observatory. The experimental setup suggests substantial increase of the areas of both muon detector and surface air shower array. We present some results of calculations of selection efficiency of air showers from primary gamma rays for different configurations of the array. It is demonstrated that by increasing the muon detector area up to 615 m$^2$ (the maximum possible value) one can reach with the Carpet-3 the world-best sensitivity to 100 TeV gamma rays.
The preliminary values of upper limits on the flux of cosmic diffuse gamma rays with energy higher than 930 TeV are also presented, derived from experimental data of the Carpet-2 shower array for a net exposure time of 9.2 years.