Also late to discussion. Certified Flight Instructor. Hoping to clear up the "lateral boundaries of Class E Airspace designated for an airport". The FAA's definition of Surface Area in the Pilot Controller Glossary is below:
SURFACE AREA− The airspace contained by the lateral boundary of the Class B, C, D, or E airspace designated for an airport that begins at the surface and extends upward.
Key words are
BEGINS AT THE SURFACE. Airports with Class E that begins at 700AGL don't fall into this, nor do the outer shelves of Class B and C as they don't begin at surface.
This issue has been extensively discussed as regards aerobatics, including a legal interpretation from the FAA.
91.303
No person may operate an aircraft in aerobatic flight—
(c) Within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for an airport;
Same key words and concepts. FAA has issued a legal interpretation that states that airspace that is not designated for SURFACE is ok for aerobatics, and thus for drones, regardless of what airspace is above. For more reading:
http://www.rapp.org/archives/2006/03/surface_area/