A device for directing gas impingement to an inner casing of a gas turbine may include a plate configured for attachment to the outer surface of the inner casing. The plate has a first surface opposing the inner casing when the plate is attached to an area of the inner casing and a second surface opposite the first surface. The plate defines a plurality of holes through the plate from the first surface to the second surface. The holes are arranged with a predetermined non-uniform distribution in the plate corresponding to a desired preferential impingement pattern for providing non-uniform heat transfer from the area during operation of the gas turbine so as to control temperature of the inner casing across the area. Various options and modifications are possible. Related gas turbine assemblies are also disclosed.