Thermal control is provided for a gas turbine casing by supplying thermal control gas from a compressor to a space between an outer casing and an inner casing, and transferring the thermal control gas from the space through the opening in the inner casing via a plurality of holes defined through a plate attached to an outer surface of the inner casing. The holes are arranged with a predetermined non-uniform distribution corresponding to a desired preferential impingement pattern for providing non-uniform heat transfer. A gas turbine thermal control assembly includes structure providing preferential heat transfer from the inner casing during operation of the gas turbine via a thermal control gas flow path from radially outside of the inner casing into the interior of the gas turbine.