What stat determines how many spells are drawn when you use draw?

Or an exploitable game mechanic that makes it easier to gain access to Diablos as soon as you receive the Magical Lamp.

Preety sure when I had a very high mag stat for quistis on one play-over she was drawing 7-9 spells per draw. When zell, who I focused on increasing his str and vit, drew magic he got 1-4 very more often then he did anything above 7 and never 9.