QUOTE (James McMurray @ Jun 16 2011, 07:54 AM)

Its easy to understand, and is a perfectly logic and well formed argument. Unfortunately the only thing saying that planar boundaries restrict all sorcery is you. No rule for that has been supplied.
Also, I'm not saying you can defend across the barrier. Its a gray area and I won't make a decision until I have to, at which point I'll rule in favor of the PCs unless they want it to go the other way. From then on out we'll follow that ruling unyil a real one is found or it turns out to be unbalancing.
My argument is against your lack of proof, not in favor of either side.
Since you cannot target spells across a barrier, how can you target the spell across the barrier with Counterspelling? It really is as simple as that.
Lack of Explicit Evidence saying that Counterspelling does not Cross barriers does not mean that it does. In fact, it is heavily Implied that it does not. Why should it have to be explicit? We know that active Counterspelling (Dispelling) cannot cross barriers. Why, then, should Passive Counterspelling (Spell Defense) be more powerful, especially since there is no need to defend across the barrier because you cannot even be targeted across the barrier? The explanation is Simple; It isn't.

No worries, though...

Oh, and a Quote here indicates What
Sorcery is not capable of doing.
QUOTE
The Limits of Sorcery
Currently, sorcery obeys the following limitations, which form the base-line assumptions
according to which all spells in this and other Shadowrun books were created. Players and
gamemasters may choose to ignore or alter any or all of these assumptions, but doing so may
unbalance their game.
Sorcery Cannot Affect Anything to which the User Does Not Have a Magical Link.
Sorcery Cannot Alter the Fabric of the Space/Time Continuum.
Sorcery Cannot Divine the Future with any Certainty.
Sorcery Cannot Summon or Banish Spirits.
Sorcery Cannot Raise the Dead.
Sorcery Cannot Create Magical Items.
Sorcery Cannot Bridge the Gap between the Astral and Physical Planes.
Sorcery Cannot Create Complex Things.
Magic Is Not Intelligent.
These are the Rules by which Sorcery exists in Shadowrun currently. Note that the Rules do not say Spellcasting, they say Sorcery. Again, Counterspelling is a Subset of Sorcery.