Concerning "concept of place", Avi is interacting with a foreign computer via Internet, or the equivalent. That means he is using the equivalent of a Universal Resource Locator to access the information from the equivalent of a a Domain Name System. For the information to come to him, he must also appear as being at a Domain Name System, or the equivalent. This is how we define "whence" information comes and "whither" it goes. However, this kind of "where" is not impacted by geography. Avi "exists" in two different worlds at this moment; the holy ground exists in one of those, but the other does not have holy ground. That means he can be "found"--"located"--within the cyberworld in which he is operating.
I would say that he cannot be found within the geographical world in which he is also located--your position cannot be traced to him, because that requires crossing between worlds. As you noted, the nearest node outside the protected area can be identified, but not the spatial coordinates of your wireless connection. However, Avi is vulnerable to magical attack.
I would suggest determining whether Avi is atheist/agnostic in an active sense. I know that Whisp's computer is completely atheist (it refuses to believe that he can work magic even when he works it, nor that anything that impacts them could be magical). That would afford the computer a certain bit of protection against magical attack (and as you've demonstrated, it is possible to use magic through the connection). I do not believe that the magic could leave Avi and impact anyone in the Holy Ground--but that does not mean that Avi could not be remotely influenced to take actions which would affect people there. The negative side of determining that Avi is atheist/agnostic is that you could not discuss using magic with him (he would not comprehend it and think that that part amounted to doing nothing) and he could not cast spells (which possibly he cannot do anyway).
In short, Avi's cyber location could have been compromised such that Avi can be targeted by magic or technological attacks; Avi's geographical location is probably protected by the holy ground, but a trace could get as close as the nearest point on the line outside that holy ground and might be close enough to put you in danger.
I would be thinking in terms of how to create magic that will work in cyberspace, and how to cast it there.
--M. J. Young