Growing hordes packsize calculations are not correct

It seems to be that the calculations for packsize with growing hordes and gilded scarabs is off. For example earlier i ran a 30 packsize with the below modifiers:

30% increased effect of modifiers from atlas tree = 9% packsize
Shaping the valleys = 10% packsize
Growing hordes with 4 gilded scarabs = 60% packsize

That should total to 109% packsize, unfortunately it ended up being 20% below that sitting at 89%, i've ran a few more maps and noticed similar results. Which makes me assume that they only count as 10% packsize each instead of the 15% like it says on the atlas tree..Or i'm extremely bad at maths!

I haven't tested the other rarities of scarabs, so i'm not sure if their values would be off too :D