Hi Chris.
For sit down gigs (most of them) - often small jazz gigs - I wear them belt mounted. For stand up gigs usually on my shirt collar. I should probably clarify the word 'muffled'. Its a massive over-emphasis on bass and low-mid frequencies that I feel swamps vocals. They don't distort or anything like that (although, as I said most of my gigs aren't that loud). So I end up in post production heavily reducing bass frequencies and upping vocal type frequencies, in fact a hell of a lot of messing about....what I then end up with isn't dissasterously bad although it isn't brilliant compared to other peoples recordings.
At first I thought maybe its my placement, or the sound quality of the gigs I go to but I dont think it is. If I do a test where I record my hifi at top volume the Sony although a little tinny and lacking in bass produces a much preferable recording to the CA11s which sound 'muffled' The results are independent upon whether I connect to my minidisc or my Tascam.
If I'm using the Tascam 07s inbuilt mics on this test they sound (to my ears) vastly superior to both...although I haven't tried it at a real concert, I will next time. I would still be interested in any 'cheap and cheerful' recommendations