Question on FT missiles, caused by a new Player

With Missiles both MT and Salvo:

Does the words "within 6mu" mean within a 6mu Radius or a 6mu Diameter? 
I 
know the answers in the archives, but where theer are a # of playtesters
whop 
uses this list.  I hope that he will be happy with this list answer..

Have a Good One,

DOC Agren

     (Lurker on the Digest)