Active clearance control systems for gas turbine engines are disclosed. An example active clearance control system may include a generally circumferentially mounted spray tube comprising a plurality of impingement holes arranged to impinge thermal control air on a clearance control component of a case; a rigid mounting assembly substantially rigidly coupling the spray tube to the case; and/or a sliding mounting assembly coupling the spray tube to the case while permitting limited relative movement between the spray tube and the case in a direction generally parallel with an engine axis. The sliding mount may be coupled to the case generally axially forward of the rigid mount. A ratio of the stand-off distance to the impingement hole diameter may be less than about 8. A ratio of the arc spacing to the impingement hole diameter may be less than about 15.