Am I incorrect in saying that you can only target one representative of the target?
For example: Individual can only target one individual.
Group can only target ONE group (two units in an army separated by a distance, you could only target each individual unit, not the entire army.)
Room, only one distinct room.
Structure only one distinct structure.
Boundary only one boundary.
Here's the main issue, though: Can one, with enough Size mods, target the entire Lunar Sphere if they're in an otherwise unbounded space.
For a less insane example: A valley with a lake. Could the lake be a separate boundary within the first?
There's some scary implications in your question. Interesting one too.
Let me make sure I am reading correctly though: are you asking about the possibility of subboundaries within a boundary? Using your valley example: would a spell aimed at the valley affect what was in the lake since the lake was it's own distinct boundary?
If I am understanding you correctly, I would say regardless of what could be considered a subboundary within the target, a spell with Target: Boundary effects all within the target. If I cast a spell with target of room, someone could not hide in the cupboard sitting in the corner and state it was a seperate space. The cupboard might help protect against a physical effect of the spell, something going boom, but a spell to make everyone in an area go to sleep will still get the person in the cupboard.
If I did not read the question correctly, sorry for the long post.
I'm not sure what the "target" would be here, since one cannot target "an area" (unless they are Creating something in that spot.)
But, in theory, yes - if you had enough "x10 size" modifiers, I suppose one could cover "everything" - tho' that is huge beyond imagining. (A "How many wizards can dance within the Lunar Sphere?" sort of question.)
So long as an area fits the definition of a "boundary" (p 113), you can have Boundaries within Boundaries within Boundaries, ad infinitum. For instance, one could have a lake within a garden within a walled city within a valley within a forest - each a larger "boundary" than the next. Up to the mage at the time of casting which s/he will affect.
There is at least 1 cannon spell that a group isn't strictly a group...
ARC OF FIERY RIBBONS
R: Voice, D: Mom, T: Group
A dozen multi-hued ribbons of flame leap from your hands and fly out as far as your voice carries, covering a 60-degree arc. All those in the arc take +10 damage.
(Base 5, +2 Voice, +2 Group)
So as long as your level modifiers are reasonable, and your discription is clear then at the very least a "group" doesn't have to be a Group.
This is a creo spell that creates something, the "group" is the group of fiery ribbons, not the unfortunates who are burned by them. This particular example is a strict group as defined in the rules.
You can not get around the target definition with a fancy description (you have to do it with a non-standard target).