iCandy, I am in the same boat as you are.
Here is what I found from the ManhattanGmat's forum. This was the response of one of the instructors:
"Which" can be a little tricky. The rule is that it has to refer to the closest preceding primary noun. It's often the case that this is the immediately preceding noun, but not always.
So, when is the primary noun not the immediately preceding noun? When some description needs to be attached to that primary noun to explain it adequately.
She agreed to cover the cost of the tickets, which was very high. -- technically referring to cost b/c "of the tickets" is a description of the type of cost
It would be cleaner, though, to say "She agreed to cover the tickets' cost, which was very high."
Sometimes, we can't easily move the descriptor noun earlier as a possessive (as we did above) and we have to keep it as a prepositional phrase. eg:
After falling down in the middle of the runway, she maintained her aura of detachment, which inured her to the laughter. We wouldn't say she kept her detachment's aura - we have to use the prepositional phrase there, but the "which" clause really modifies aura, not detachment.
You'd be unlikely to see something like your sentences on the official test b/c it's a bit too complex. Most of the time (on the test), if this issue comes up, it will be presented as a single prepositional phrase following the primary noun.
To find what you seek in the road of life, the best proverb of all is that which says:
"Leave no stone unturned."
-Edward Bulwer Lytton