Traditionaly whole cone hops are used for dry hopping. IMHO- pellets could contrigute astringencey (more than whole) because they are all torn up and the alcohol could extract tannins in finished beer. Dry hopping can also give a "tea like flavor" from the vegitable matter when over done.
Otherwise look @ the Co-humolone of the bittering hops. Also first wort hopping has impericaly been know to give a smoother bitterness but I havent read any hard data on that. Personaly use mostly "aroma" hops, Norther Brewer being about the highest Alpha, because I feel the other verieties are "smoother".
Last- balance hoppy beers with some residual gravity- maybe its too dry?
Off topic- Firewaters in AC is selling Bithering Idiot barley wine in Pints!!! Very dangerous for us malty beer lovers :-)
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