I recently looked at the map in Sanctuary of Ice, the 4th edition book, and compared it to Guardians of the Forests. Where exactly is the tribunal border between Rhine and Greater Alps? The covenant we're using is just on the south bank of the Rhine, east of Basel. Which tribunal will this fall in?
E.
Oh, that's an easy one:
in your saga the border goes north of you if you don't want to bother with the stuff in the Rhineland, and south of you if you don't want to bother with the stuff in the Alps, and kind of around you nebulously if you want to be involved in border clashes and disputes.
Which is to say (as the guy who nominated where that border is) : for your personal game, it doesn't matter.
For my game, the border is Basel: that is, if you are above the navigable Rhine, you aren't in the Rhineland anymore. That being said, for your game, it shouldn't matter. The border should move to suit your stories, not the other way around.
I always figured that, as with most medieval "states", there are not so much borders between tribunals but rather frontiers. In other words, there are not hard-and-fast lines of demarcation, but "zones of influence".
Look at the accuracy (and lack thereof) of most medieval maps... 
I love the fact that the borders aren't very precisely defined.
My upcoming saga is a continuation of an old one, because a lot of cool stuff happened (and I can't invent something unique again and again), we will base it in same Trinubal. But we're looking for something completely different. First saga was a wilderness covenant in Cornwall at the Channel coast. Second one was in central France, also wilderness (at first, but then the huts grew into a village...).
This new one will be an Urban covenant in a market town. At first I thought Brügge, but decided to completely change style.
So I defined a small part of France at the Mediteranean coast, just west of Italy, is a place lost or perhaps still disputed between Normandy, Provence and Rome tribunal - currently Normandy "controls" it. But this dispute is a covenant Hook.
Ah, this makes it more interesting. I added the Hook Tribunal Border to the covenant, so this one will be pressed right between the two tribunals.
What kind of conflicts would happen between Rhine and the Greater Alps? The way I understand it, the Greater Alps Tribunal won't allow any new covenants in their tribunal.
Any ideas for how the two tribunals would try to affect the covenant? 
E.
First things that spring to mind might be efforts on the part of covenants within the Greater Alsp Tribunal to deny or otherwise contest any and all Vis sources in the immediate area, causing serious conflicts for your covenant's magi when they go seeking Vis.
Another might be demands from both tribunals for services on the part of the magi as recompense for their presence on contested land.
Attempts by covenants of both Tribunals to secure the votes of the magi at the Great Tribunal Gathering.
Minor feuds between other individual covenants either from one or both Tribunals that catch your covenant's magi in the crossfire, might be abnother potential story seed.
I think it is written in the core rule book ... or in HoH TL (?) (serf's parma!) that there are no fixed borders. Wether a convenant belongs to a certain tribunal or to another ist the choice of that convenant.
I have got to check on this tonight.
I confirm, although I can't tell precisely where it was. Noble's parma: TL, in the guernicus chapter.
Fixer wins the parma contest 
page 60 HoH:TL
Another reference is in HoH TL page 49, in the section about voting. I don't recall the exact wording but it states that most Guernici oppose any attemp to force a covenant into a certain tribunal. However, most does not mean all, and the notion of Guernici becoming involved in a border quarrel looks like a great story hook.
So choose as you like in your saga.
Oooh, I can see story potential for my Saga, set in NW Bulgaria pre-Asen rebellion (1180). Since the Transylvanian Tribunal is dominated by the Tremere, there could be reason for the player magi (all Mystery Cult Houses) to "move" their covenant into Thebes. I'm not using the Tremere as villains, but their tight grip on Transylvania will be an inevitable issue to address.