Hose length should only be an issue for foaming during serving and not for carbonating. Seems you would need to be below 40F to carb at 12psi (I don't have a chart handy). Try increasing the pressure to 25psi for 24 hours and see if things improve.
Something is always fermenting....
"It's Bahl Hornin'"
Kegged: Bourbon Barrel Imperial Stout
On Deck: German Lager