Buddy,
I saw (or read, its been a while) where bass in a tank would nose down on the edge of a lighter colored "V" painted on the bottom of the tank. Just as if it where the edge of the brush at open water.
On a river fishing trip many years ago, My Dad and I caught the tides right, and the bass where holding in the muddy water just where the clear water, and food, were coming out of the marshes. We caught 16 keepers and probably a half dozen others trailing beetle-spins out of the clear water into the muddy.
I guess the point of all of this is that what we think of as a "Break Line" has to include a few more types than the obvious.

Kirk