My interpretation is that the real transmission occurs at the meeting of a master's realisation and a student's devotion, as it were, the coming together of these two. As such that cannot be impeded by distance or diluted by numbers of people etc
If one accepts that the other circumstances are subordinate to these two essential criteria (the Guru's realisation and the student's devotion), then the scope for authentic transmission to occur in all sorts of circumstances and situations is there.
Conversely if those two criteria are not met, then no amount of jostling one's way to the front row, making sure that one has reserved a cushion right in front of the guru, directly in the line of fire, during an empowerment will really any difference, if you see what I mean.
So regarding drawing a line, I think that the line is drawn by ourselves in the sense of how much we have opened a channel of connection with the guru by our devotion.
If that's there, so is the transmission.
But of course our devotion can be a bit conditional at times, well mine certainly can, so it can be influenced by being in the physical presence of my teacher, or a situation I associate with Dharma, but that's my projection, and more to do with the conditions, ie personal preferences, that I impose upon the path. That's where a lot of the greyness is.
A lot of these discussions involve concerns about tradition, or rather the break from it. And there is validity in that kind of consideration, but I can't help feeling that if a master such as, for example, ChNN decides that webcasts are valid methods of transmission, then they are. I just can't conceive the possibility of him leading anyone astray or duping people into thinking they have received something when they haven't. That is not what he, or masters like him are about. That for me is reason enough to trust authenticity of these kind of transmissions, but I accept that decision to trust has to be made personally by each of us.
And if we accept the stories of transmission via footwear abuse and conversations about dogs barking because they are historical, why should we question the potential efficacy of transmission via webcasts and other modern technologies...
I'm sure not everyone will agree, many will find this a bit woolly...but I really think the quality of transmission is governed by devotion.