I am a dealer for Mountain High Equipment and have installed several ASW-27 systems. Contact me at: info (at) mmfabrication )dot) com if you don't get the information you need from RAS.

The ASW-27/29 will only accept a steel cylinder of a particular size, and the regulator mounts at a 90 degree angle to the cylinder. It usually has sufficient clearance to the seatback (if the regulator is angled slightly outboard). The interference is usually the large cast aluminum handle that opens the valve on the cylinder. Either remove the retaining screw on the handle and only use it to open and close the cylinder valve before and after flight (use a string to keep it attached so you don't lose it) or make a simple one-wing handle that will not interfere with the seat back. If you need a handle and don't want to make one yourself, contact me.