Does the Lagrange L1 point have a 'size'? Like in cubic kilometers, what is the size of L1 "area of influence"? being unstable I guess that size can vary?
From this source I get: 


  The size of these islands varies. Each planet in the solar system has
  its own Lagrangian points. The islands of stability get bigger farther
  from the Sun and also for more massive planets. The ones associated
  with Earth are roughly 500,000 miles (800,000 kilometers) wide. The
  biggest zones (at least in the solar system) are Neptune’s; they are
  about 2 billion miles (3.2 billion km) across.


L1, L2, and L3 are unstable. If a Sattelite ventures too far from the Lagrangian area it will fall towards the sun. As you can see from the image below. This image came from the source linked above.