Watch the 1 5 6 3 Structures online guitar lesson by Brad Carlton from Guitar Lab: Open String Universe

This lesson uses a root fifth sixth third structure on the 6th through 3rd strings combined with the 2nd and 1st strings open.

Voicing 1 is a B6add4 voiced 1 5 6 3 1 4. Ionian and mixolydian fit this chord. You could also think of this chord as an EMaj9/B voiced 5 9 3 7 5 1. Ionian and lydian would then apply. Voicing 2 is a CMaj7/6 voiced 1 5 6 3 7 3. Ionian and lydian fit this chord.