Defaults read/write question

OSX 10.9

How does "defaults" know where to look for .plists? To expand:

defaults read com.apple.finder
is located in ~/Library/Preferences

but,

defaults read com.apple.mail
is located in ~/Library/Containers/com.apple.mail/Data/Library/Preferences/com.apple.mail.plist

So my question is, what does 'defaults' use to locate the appropriate .plist and is there a way for me to have it output the path for vicariously placed .plists (such as mail)?

Thanks!