The Standard Riff can also be found with the tonic on the 5th string.

On an A chord you can find the A tonic on the 12th fret of the 5th string.
We would be playing the third blues position here normally.

Play the tonic on string 5 with your pinky.
Play the hammer-on from the minor to the major third with your ring finger.

Because we’re moving with the chords, we can find the D and E version (IV and V chord) of the standard riff very close to where we found our first S.R. in the 1st blues position.

That is because the tonic of the D chord can be found on the 5th fret of the 5th string and the tonic for the E chord on the 7th fret of the 5th string.