They don't really care that much
In the past I have researched potential future slots, and then approached my Postings Officer about it. In person he was positive and grateful for my enthusiasm, even stating with a smile and a handshake "You've done my job for me."
However the promised paperwork never arrived two weeks later, and as the months flew by, as did my unanswered emails and telephone calls, he instead decided to shaft me with an extension of my tour.