The scatter shot has no range increment and doesnt benefit from distance.
If you are looking at increasing the area of effect on a scatter ability work with your GM to base the pricing on the 'Widen Spell' metamagic feat, which places a +3 level adjustment on spell level (so expect it to be pricey)
so long story short.... no way in hell do you get a 30ft cone for a +1 enchantment cost.