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 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 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 (L1) in a direction between an inner diameter position (ID) of the opening and an outer diameter position (OD) of the perimeter which is greater than 70 percent of a second radial length (L2) between the inner diameter position (ID) of the opening and the outer diameter position (OD) of the perimeter . 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 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 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 (L1) in a direction between an inner diameter position (ID) of the opening and an outer diameter position (OD) of the perimeter which is greater than 70 percent of a second radial length (L2) between the inner diameter position (ID) of the opening and the outer diameter position (OD) of the perimeter . <EOS>