It seems like the person choking the victim will need to be close to the victim he/she wants to force choke without looking at the victim.
As shown in this example.
'Some individuals were also powerful enough and experienced enough to not require any visuals to kill someone via force choke, such as when Letta Turmond's Jedi backer, later revealed to be Barriss Offee, killed her via a force choke and subsequently framed Ahsoka Tano for the deed.
As well as when Darth Sidious used the ability to kill the Shadow Collective guards standing near the door before opening it to confront his former apprentice, Darth Maul and the latter's apprentice, Savage Oppress.
With visuals it seems they can choke the victim from a long distance away.
ESPECIALLY - Darth Vader was also seen using this ability to express his dissatisfaction with an Imperial officer during one of his Jedi hunts, choking the man while staring pointedly away from him.'
Sorry, the link is here: http://starwars.wikia.com/wiki/Telekinesis