Tested the passive effects of all 4 spirits at level 3, according to wiki they should have a
(JobLv ÷ 2)% chance to cast a bolt spell at level
Floor(JobLv ÷ 10)
1. Summoned agni lvl 3 and activated spirit control 1 to make it enter passive mode
2. Attacked eggs and watched autocasting of firebolts, noticed they were being casted at random levels.
3 Repeated steps 1 and 2 for aqua, tera, and ventus lvl 3, results were the same.