Roadrunner,
Some mics are actually designed to be placed in the corner of your mouth between your lips and are shaped as such.
The one that I have is definately designed this way and I have never been accused of being garbled, furthermore the rig is 17 years old, although the mic has been replaced several times. May I suggest improper maintenance, having the mic to far away from one's mouth, faulty coms, poor soundproofing as well as a host of other reasons cause people to sound garbled.
Cheers, HH.
PS: Of course a few elocution lesson's for some people would'nt go astray.