ummmm...it depends.... different songs have different characteristics, different parts of songs have different levels....if you are looking for a "rule" there ain't one. Really!
Reminds me of a radio conversation I heard on teh radio 5 years ago when I was working on the arctic between a pilot coming in and the person on the ground.
Pilot: "what's the weather doing over there?"
ground:" some clouds, some blue sky"
Pilot: "ummm....where are the clouds? what's the visibility?"
ground: "I can see just fine"
Pilot: "Ummmm, but will I see the airstrip from 1000 ft? How about those mountains all around you?"
Ground: "the mountains are there"
Pilot " Okay, how about the wind?"
Ground "Yes"
Pilot " Yes? How much? where's it coming from?"
Ground "It's windy, blowing from teh left"
Pilot (who is still 100 miles away) " Would that be your left, or my left?"