Hi - I don't think it's just the number of folds, but also the suppleness of the bellows: my Jeffries 6-fold extends to 12 inches, whilst my Lachenal 6-fold only extends to 10 inches. Meanwhile, my Marcus 7-fold extends to 14 inches. If you divide these by the number of folds (actually, the channels - so a 6-fold has 7 channels),then the Marcus is best at 1.75 inches per fold, and the Lachenal worst at 1.43 inches.
Each of these boxes is fully played in.
.... but a very experienced mate of mine makes a valuable point - that learning to play with limited air is a very good discipline: you don't just waste air on bass chords, but you choose your harmonies carefully.