How wide apart is aero handle

[novetan]

I just purchased an aero bar and i hv no experience how wide shall I fix the aero handle apart. My drop bar width is 400mm shld you guys need any indication

 

[MichaelW2]

Any width you like.
Shoulder width is used for a neutral elbow bad location.
Narrower is more aerodynamic.
You may also re-asses your saddle position, maybe rotating along an arc centred at the BB, forward. UCI have limits on this, but triathlon don't.