[@WildChocobo]
Number of generations on the family. 

Why would the family bother training three heirs? There's a reason Sakura was sent off to the Matous and why some magus families put a bunch of four years olds into a deathmatch to decide which kid is worth training. 

Why does this magus family exist if they have no conceivable theme or path to the Root? The whole point of making a Magic Crest is so that your successor can continue your research. 

You can't use other elements besides earth. 

Details on Bounded Field capacities.