Some quick Google-fu regarding CO2 permeability suggests that even using thin walled vinyl lines and going a week between pours there shouldn't be significant change in carbonation in the lines. There's something else going on, like maybe an uncooled tower, warm shank, etc. Whatever it is, it's not the line length.
I'm trying to find some porn filmed by a dog wearing a GoPro. - SharonaZamboni