Where to capo for B Lydian
Put the capo at fret 6 and play B Lydian using E# Lydian shapes. That is the easiest of the eight positions ranked below, and it is what most players reach for. Against playing B Lydian open, it drops the mean difficulty of the key's seven chords from 5.6 to 3.4 and gains 16 ringing open strings.
You want B. Capo 6 and play in E#.
All eight positions, ranked
Each row transposes B Lydian down by that many frets to find the shapes your hand would actually make, then scores the best voicing of all seven chords — fewer fingers, less stretch, closer to the nut, fewer muted strings. Lower is easier. Standard tuning (E2 A2 D3 G3 B3 E4).
What you are playing
The seven chords of B Lydian are B, C#, D#m, E#dim, F#, G#m, A#m — the ones the ranking above is scored against. Their diagrams are on the B Lydian key page.