Beagle. I believe the reheated Javelin actually suffered reduced reheat power at LOW altitude. From memory, it was because the early two-position (area) nozzle had to be optimized for a dry power setting at low altitude and, a reheat power setting at high altitude. Probably the best compromise but, reheat at low altitude cosequently gave such a mismatched nozzle area that overall thrust reduced.
OAP