A combustor of a gas turbine engine, the combustor comprising: a combustor shell comprising a diffuser side facing a diffuser chamber and a combustor side facing a combustor chamber; a first combustor panel coupled to the combustor side of the combustor shell; and a second combustor panel coupled to the combustor side of the combustor shell, wherein a gap is defined between the first combustor panel and the second combustor panel, and the combustor shell comprises a gap impingement hole (145A, 145B) that is directly open to and is configured to deliver cooling air directly to the gap, the combustor further comprising a throttle plate coupled to the diffuser side of the combustor shell, wherein the throttle plate defines an intermediate chamber with the diffuser side of the combustor shell, the throttle plate comprises an orifice hole that is open to and is configured to deliver cooling air from the diffuser chamber to the intermediate chamber, and the gap impingement hole (145A, 145B) is open to and is configured to receive cooling air from the intermediate chamber, wherein, a first annular cooling cavity is defined between the first combustor panel and the combustor side of the combustor shell; a second annular cooling cavity is defined between the second combustor panel and the combustor side of the combustor shell; the first combustor panel comprises a first support rail extending radially from the first combustor panel to displace the first combustor panel from the combustor side of the combustor shell; the second combustor panel comprises a second support rail extending radially from the second combustor panel to displace the second combustor panel from the combustor side of the combustor shell; and characterized inthat the flow of cooling air across the gap from the first annular cooling cavity to the second annular cooling cavity is at least impeded by the first support rail and the second support rail, wherein the gap impingement hole (145A, 145B) extends through the combustor shell in an angled direction. a combustor shell comprising a diffuser side facing a diffuser chamber and a combustor side facing a combustor chamber; a first combustor panel coupled to the combustor side of the combustor shell; and a second combustor panel coupled to the combustor side of the combustor shell, wherein a gap is defined between the first combustor panel and the second combustor panel, and the combustor shell comprises a gap impingement hole (145A, 145B) that is directly open to and is configured to deliver cooling air directly to the gap, the combustor further comprising a throttle plate coupled to the diffuser side of the combustor shell, wherein the throttle plate defines an intermediate chamber with the diffuser side of the combustor shell, the throttle plate comprises an orifice hole that is open to and is configured to deliver cooling air from the diffuser chamber to the intermediate chamber, and the gap impingement hole (145A, 145B) is open to and is configured to receive cooling air from the intermediate chamber, wherein, a first annular cooling cavity is defined between the first combustor panel and the combustor side of the combustor shell; a second annular cooling cavity is defined between the second combustor panel and the combustor side of the combustor shell; the first combustor panel comprises a first support rail extending radially from the first combustor panel to displace the first combustor panel from the combustor side of the combustor shell; the second combustor panel comprises a second support rail extending radially from the second combustor panel to displace the second combustor panel from the combustor side of the combustor shell; and characterized inthat the flow of cooling air across the gap from the first annular cooling cavity to the second annular cooling cavity is at least impeded by the first support rail and the second support rail, wherein the gap impingement hole (145A, 145B) extends through the combustor shell in an angled direction.