The SR-71 refused to give its exact altitude, the concord seems to vary its altitude within a 5000 ft band as tempretures changed, but still well above other ai

The SR-71 refused to give its exact altitude, the concord seems to vary its altitude within a 5000 ft band as tempretures changed, but still well above other aircraft. The traffic controller simply wanted to ensure the SR-71 stayed well away from the concord.