I tried using box 1 at the 5th but it doesn't sound right.
You would actually play Box 1 with your first finger at the 2nd fret (F#m= Relative minor of A Major) with your
pinky on A at the 5th fret to play A Major pent.
Box 1 with your
first finger on 5th fret A would give you Am, but would also be
C Major (Relative Major) from your pinky.
1st finger on A = A minor (& C Major)
Pinky on A = A Major (& F#m) = Box 1 "shifted down" 3 frets from A to F#
The "infamous" 3 fret rule.
Every Box is both Major and its relative minor.
The
chord you are playing over will be the determining factor, not the box.
If you play A minor Box 1 over an A7 or Am chord, it will sound minor (A minor).
If you play the exact same A minor Box 1 over a C or C7 chord, it will sound Major (C Major).
To sound A Major over an A7 or A Major chord you would move Box 1 down 3 frets to F# or play Box 2 from A.