Carulli op. 8 flute and guitar concerto.

I am under the impression that this concerto is easier to play with a capo on the third fret. There are very few notes below G on the sixth string. Is there any chance that this concerto was conceived -at least in the beginning- for a terz guitar ? There is a section in G minor. That's an unusual key for a guitar, but using a capo in the third fret you get the more guitar-friendly e minor.