I understand that I'm doing math on what may be essentially a jargon issue, but still...

I'm developing my own calculators for speaker coverage patterns and have been trying to integrate the "50% coverage" and "20% coverage" benchmarks...  but what are these percentages meant to refer to?

They don't seem to refer to the ratio of overlapped area of a neighboring speaker to a single speaker's coverage area.  The math was kinda painful, but in the end wasn't close.   (In any case, a "50%" overlap pattern overlaps noticeably less than 50% of its neighbor... just by eyeballing.) 

My gut assumed the following: given a line through the centers of two equal and overlapping circles; the ratio of the line length falling within the overlap to the length of the circles' diameter."  This means the 50% works.  (The neighboring pattern overlaps by half - 50% - of the diameter of the circle.)  However, the 20% figure should actually then be about 29.3% by this math.  More precisely:  ((-1 * SQRT(2))+2)/2.

I wonder if perhaps this is supposed to represent the aggregate amount of overlapped area within the pattern?  I haven't tried calculating that, but I'm willing to try if that's the intention.  But starting and ending where?  Within a square/rectangle defined by the centers of the outermost speakers, as shown here? (Edit: I solved it below as well.)

Does anyone know where these terms originated or what math they purport to represent?

(Update:  In the above image,  25.56% of the square is covered by overlaps in speaker coverage.  Looks like this is not the solution to my query, as the pattern is 'looser' than the "20%" overlap pattern.) 

(Update: I ended up solving the overlapping area by percentage for several different permutations of overlapping circles and bounding squares.  I didn't come up with anything that would match the "50%" and "20%" patterns.  See Below.  My calculated percentages are in the lower right of each bounding box.)