I heard a presentation years ago (Perhaps at the International Citrus Congress in Sun City South Africa, 1996???), about Flying Dragon from seed. They said that while it was highly nucellar, there was a lot of variation among seedlings. As I recall, they said that there was a nice correlation between the degree of thorn curving and the amount of dwarfing you could get as a rootstock. So they recommended selecting in favor of the most curved thorns, if strong dwarfing was the desired characteristic in the rootstock.