Why does bbbox start on G string F note for an A minor song

[Orange Cowboy]

In Irresistible Phrasing 101 Mod2 - the backing track is in A minor.
From Guitar Grid Mastery I thought you choose the string based on the low E string fret - in this case 5th fret is A
but A doesnt sound as good as the G string 9th fret
the low E string 9th fret is a C#

Certainly I can just slide around until I hear the right notes - though I wonder what the theory is behind it.

Thanks in advance

 

[Alan Desmond]

If you look at Am pentatonic you will see the bb king box is part of pattern 2. Maybe you:be not got to grid mastery unit but you can play from any key note. Not just the low e string. Suggest you play it from the octave of A at fret D7. Lots of music nice when you play the pattern of the particular song or riff from different octaves. Just don't forget to make any adjustments for B string warp zone.  Suggest you also google house of blues and Eric Clapton 1968 stock riffs.

Hope this helps. Enjoy the variety of different position play.