Area of Effect passives

Area of effect passives are not increasing the effective area in the amounts they said they should.

I'm currently using Bone Blast, this skill says it has a base area of 1MT i have the weapon on 20% quality so the area goes up by 0.4mt to a total of 1.4mt, at this point everything works like it says.

I got 4 passive nodes to increase area of effect, 3 "Spell area of effect" and 1 "Reverberation", the 3 "Spell area of effect" each give 8% increase(24% total), "Reverberation" gives 20% for a total of 44%, the area of effect of the spell is currently at 1.6mt, if you only consider the passive bonus to apply to the base spell area it should be at 1.4mt base + the 0.4 of the quality on the weapon, since that effect is not a multiplicative, it adds 0.4 to the base.The area of Bone Blast at this point should be 1.8 and not 1.6, getting 44% of area of effect gave the skill only 20% of increased Area.

So spell area effect is either not working like it should of the calculation is done differently and not said anywhere.