What the hell? Lack of line of sight is not the same as invisibility. That's absolutely wrong.So, you're telling me that invisibility confers additional benefits besides making one invisible? First, I've heard of that.
If you prefer another way, hearing a moving creature is DC 10 (PFRPG 102), which is amazingly enough the same number you get if you were to use perception to notice a visible creature DC 0, add +20 for invisible, and subtract 10 for moving at full speed.
Invisibility gives +2 to hit creatures and makes them flat footed. Counting "out of line of sight" as invisible adds hedge rules, like... archers firing from an arrow slit are counted as full cover, which is completely out of line of sight, which is now invisible? An earth elemental attacking from inside the floor is now invisible and such. That kind of thing.
"Out of line of sight" usually means behind an object, which is +10 to the DC for being behind a wall. Stacks per wall.