Watch the Half Step Below: Over Major online guitar lesson by Rob Garland from The Guitarist's Pentathlon
The minor pentatonic has a jazzy quality when played a half step below a major chord. The lick I played against the chord BbMAJ7 includes the 9th (the note C) and sustains on the #11th (E). It's important to let the sound of the notes dictate the phrasing, rather than playing stock licks. As you experiment and let notes hang against the chord listen to the moods they create and try to work through all five shapes of Am pentatonic against the BbMAJ7 chord.