Here is the way I view the E9th as a Blues-based tuning.
In the pedals down position (A and B pedals activated), I move back two frets and lower strings 4 and 8 a half tone. At that position every string except the 9th string establishes a Dominant 9th sound, which is my favorite choice for a dominant chord. In that position there are a lot of string choices from which to build Blues melodies.
Also from the pedals down position, I often move up 3 frets for tons of riffs. As before, every string except the 9th string works as a scale at that fret, and if you omit the 2nd string you get the Blues scale and the Pentatonic notes which is the primary voice I prefer when playing Blues lines.
Try this out to hear that Blues sound:
N=No Pedal…… I will list A & B symbols next to the string.
Key of C7th (at the 6th Fret)
3B 3N 1 4 5A 5 6B 7 8 10A
In between 5A and 5 you can use a half A pedal to get the Blues scale, and you can add the 2nd string into that scale for a “jazzy” touch to the Blues.
– Paul