No receiving end does force the short-range issue and does make your conjecture make sense.

Oh man, the science behind the matter/energy handwavy stuff? You really, really don't want to think about that too hard. (the energy cost! ARGH!)

I think we've seen the transfer in the series too. So, maybe the rings just take all matter within their volume and transfer it. Meaning they just swap between "empty" air and a person, so it just looks like a one-way transfer.