Looking through spell calculations, I've noticed the following problem. (Code snippet below bolded appears to be the error)
<DisplayName>Firestorm</DisplayName>
<Description>All units in target army take 8 fire damage (+4 per fire shard). Firestorm leaves a fire raging in the affected tile for 10 turns.</Description>
By the looks of the calculation I see 8 fire damage + 2 per fire shard, not the +4.
<GameModifier>
<ModType>Unit</ModType>
<Attribute>DefendableDamage</Attribute>
<AttackStat>UnitStat_Attack_Fire</AttackStat>
<Calculate InternalName="Calc" ValueOwner="CastingUnit">
<Expression><![CDATA[[UnitOwner_GetNumFireShards] * 2]]></Expression>
</Calculate>
<Calculate InternalName="Calc2">
<Expression><![CDATA[[Calc] + 8]]></Expression>
</Calculate>
<Calculate InternalName="Calc3" ValueOwner="CastingUnit">
<Expression><![CDATA[[Calc2] * [UnitStat_SpellDamage_Fire]]]></Expression>
</Calculate>
<Calculate InternalName="Value">
<Expression><![CDATA[[Calc3]]]></Expression>
</Calculate>
</GameModifier>