the distance to you does matter
it takes more time to go around an object that is far away from you (in a circle).
all the other stuff you said is alright
and you cant get the heading unless you know the distance either.
for example
if the two bearings you take are the same and you dont know range the ship could be
staitonary.
could be heading straight at you at 1 knts
could be heading straight away from you at 30 knts
and the list just goes on.
so unless you know the exact position of an object, there is no way of determing this.
actually there is a way but its very complicated.
so if you want there ya go
http://www.haptonstahl.org/ppt/tma_files/frame.htm
i know this isnt helping much but i just hate saying something withouth backing it up whit some reason.