Where to capo for A Lydian
Put the capo at fret 4 and play A Lydian using F Lydian shapes. That is the easiest of the eight positions ranked below, and it is what most players reach for. Against playing A Lydian open, it drops the mean difficulty of the key's seven chords from 4.4 to 3.4 and gains 9 ringing open strings.
You want A. Capo 4 and play in F.
All eight positions, ranked
Each row transposes A 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 A Lydian are A, B, C#m, D#dim, E, F#m, G#m — the ones the ranking above is scored against. Their diagrams are on the A Lydian key page.