Cast on X + comet - wrong energy value

Comet says on the gem, that it has a cast time of 1 sec and an additional second is added in the description -> cast time = 2 sec

Cast on X says, that the max energy is 10 energy per 0.1 sec cast time -> expected comet energy = 200

in the gem menu the comet energy is 300 - thats a difference of 100 energy