Why does this spell sometimes hit 250 and sometimes 1900?

[Imfreezing]

local combat = createCombatObject()
setCombatParam(combat, COMBAT_PARAM_TYPE, COMBAT_PHYSICALDAMAGE)
setCombatParam(combat, COMBAT_PARAM_EFFECT, CONST_ME_HITAREA)
setCombatParam(combat, COMBAT_PARAM_DISTANCEEFFECT, CONST_ANI_WEAPONTYPE)
setCombatFormula(combat, COMBAT_FORMULA_SKILL, 5, 5, 5, 5, 5, 5, 5, 5)

local area = createCombatArea(AREA_SQUARE1X1)
setCombatArea(combat, area)

function onCastSpell(cid, var)
    return doCombat(cid, combat, var)
end

 

[Tarek]

setCombatFormula(combat, COMBAT_FORMULA_SKILL, 5, 5, 5, 5, 5, 5, 5, 5)