beginning blues chrom questions

["Jason Paul Stolaruk" <stolaruk@xxxxxxxxxxxxx>]

Hi everyone,
It's been years since I posted to Harp-L (although I haven't necessarily been
lurking the whole time).  Anyway your past advice and hints and tips have
really helped me to improve and advance my playing in the past (thanks!)
I've been playing blues on the diatonic in 2nd position for about 8 years now.
I recently bought a CX-12 chrom with the intention of playing blues, but I'm a
little bit baffled as to how to approach this beast.  I have a few questions
(and I apologize for the fact that most of them are rather basic):
First, I happened to read in a book that it is essential to cover 4 holes with
your mouth and tongue block the left 3 holes.  This is REALLY awkward for me.
I can never seem to tell if I'm covering all 3 holes with my tongue.  However,
I've gotten quite good at using a tongue block on the diatonic for the purpose
playing octaves (your mouth covers 4 holes and your tongue blocks the middle
2).  Perhaps for this reason, it feels quite natural for me to play the chrom
as follows: cover only 3 holes with my mouth and block the left 2 with my
tongue.  I can feel my way around the chrom quite easily this way, but since
the book I read was adamant about tongue blocking 3 holes, I wonder if my
technique will somehow create problems for me down the line.  What do you
think?
My other questions relate to how a C chrom is typically played in blues.  Based
on the music that has reached my ears, it seems to me that a lot of blues
players only pick up the chrom to play in D and focus on the draw notes (which
together sound like a D pentatonic scale to my ears but I don't know).  Or
maybe it's not the key of D but Dmin (could someone please clarify this?)  I
don't have enough knowledge of theory to break this down myself.  (You can also
hear Rod Piazza playing chrom on Diamonds At Her Feet from the "Live at BB
King's" album, but he's playing it in Eb and I assume he's just holding the
button in the whole time.)  Next question: what position is this called
(meaning key of D [or Dmin??] on a C chrom)?  And why not just pick up a C
diatonic and play it in virtually the same way?  Is it because the tuning of
the diatonic in the lower register is a little different than the chrom?
Are there any other positions that blues players use when they play chrom?
Sorry about asking so many questions in one email.  Any hints or tips will
likely go a long way to help me get started.  Thanks a lot!
- -jason