[Harp-L] Vibrato question

I'm fairly new to the blues harp (6 months or so). I hope a few of you
can set me straight on something.
I am working on developing a decent throat vibrato, but I'm running
into trouble with bent notes. Many players I like can get a wide,
expressive vibrato on, say, and 3-draw bent a half-step to a minor third
(e.g. a Bb instead of a B natural on a C-harp, played second position). 
Mark Ford and others get a great sound from that.
When I try to add throat vibrato to a note that I want to keep bent, I
have trouble, and it sounds horrible.  Keeping the note bent interferes
w/ getting the vibrato. My question is, how do you get past this?  Do
you use tongue wiggle to get the vibrato on those bent notes? Is there
some aspect of the technique I am missing in order to apply throat
vibrato to bent notes?
Please let me know what has worked for you all. I want to make sure I'm
developing good habits here and not taking any shortcuts. Thanks in

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