To increase your chances, don't just buy a W fare, buy a Y,B,M, etc. As high as your company will allow, it's still an 'economy' ticket.

If you have to buy the cheapest economy ticket and you're doing the upfare to W yourself, and have flexibility, then try and secure R space at the time of booking.

Other than that, this thread might be one to assist you with anecdotal experience/evidence.
http://www.flyertalk.com/forum/unite...ne-2016-a.html