Re: Size of the Hookah
The size of the hookah shouldn't make a difference in how long a session lasts. What will make the difference is the size of the bowl being used, the amount of charcoal, what type of charcoal, and the heat being dispersed.
If you have a small hookah and a small bowl, concentrate on packing the bowl in a way that won't restrict air from traveling through (fluffing the tobacco in works), and use less coals with a windcover or a large piece of foil wrapped around the bowl to help manage the heat.
Hope this helps!