A combustor for a gas turbine engine, the combustor comprising: a combustion chamber defined between an inner shell and an outer shell; a bulkhead extending between the inner shell and the outer shell, the bulkhead comprising a plurality of impingement cooling rings, each impingement cooling ring of the plurality of impingement cooling rings comprising a plurality of impingement cooling holes extending through the bulkhead; and a heat shield panel comprising a first surface facing the combustion chamber and a second surface opposite the first surface and facing the bulkhead, the heat shield panel mounted to the bulkhead so as to define an impingement cooling chamber between the bulkhead and the heat shield panel, the heat shield panel further comprising a perimeter (88, 90, 92, 94) and an opening extending through the heat shield panel between the first surface and the second surface, the opening centered about an opening center axis, the heat shield panel further comprising a radial portion between the perimeter (88, 90, 92, 94) and the opening, with respect to the opening center axis, wherein the plurality of impingement cooling holes of each of the plurality of impingement cooling rings are directed toward the radial portion of the heat shield panel, wherein the radial portion is free of penetrations; and characterized in that: the radial portion has a first radial length in a direction between an inner diameter position of the opening and an outer diameter position of the perimeter (88, 90, 92, 94) which is greater than 70 percent of a second radial length between the inner diameter position of the opening and the outer diameter position of the perimeter (88, 90, 92, 94). a combustion chamber defined between an inner shell and an outer shell; a bulkhead extending between the inner shell and the outer shell, the bulkhead comprising a plurality of impingement cooling rings, each impingement cooling ring of the plurality of impingement cooling rings comprising a plurality of impingement cooling holes extending through the bulkhead; and a heat shield panel comprising a first surface facing the combustion chamber and a second surface opposite the first surface and facing the bulkhead, the heat shield panel mounted to the bulkhead so as to define an impingement cooling chamber between the bulkhead and the heat shield panel, the heat shield panel further comprising a perimeter (88, 90, 92, 94) and an opening extending through the heat shield panel between the first surface and the second surface, the opening centered about an opening center axis, the heat shield panel further comprising a radial portion between the perimeter (88, 90, 92, 94) and the opening, with respect to the opening center axis, wherein the plurality of impingement cooling holes of each of the plurality of impingement cooling rings are directed toward the radial portion of the heat shield panel, wherein the radial portion is free of penetrations; and characterized in that: the radial portion has a first radial length in a direction between an inner diameter position of the opening and an outer diameter position of the perimeter (88, 90, 92, 94) which is greater than 70 percent of a second radial length between the inner diameter position of the opening and the outer diameter position of the perimeter (88, 90, 92, 94).