[Neus]

Thanks for testing this. Something to note is that Greaper applies uniquely with Exgalfa; it will apply its multiplication after Exgalfa receives its bonus or reduced damage, and to the individual damage per fireball. So basically, with your stats;

21+10+71+50 = 151

151 / 8 = 18.875 (18)

On lucky fireball: 18+15 = 33
On unlucky fireball: 18-15 = 3

33 x 1.3 = 42.9 (42)
3 x 1.3 = 3.9 (3)

This is before resistance, of course, but it's possible you might have forgotten one of the modifiers, such as Pure Power, tome material bonuses, -mancy bonuses, and so on.