Growing Horde Pack Size Amount Less Than Expected

I was testing Growing Horde earlier, and noticed the packsize increase is lower than it should be for both Polished and Guilded Scarabs.

Rusted scarabs work as intended, and give 5% pack size.

Using single polished scarabs in map device grant 7% pack size, rather than the listed 10%. Putting in single guilded scarabs only grant 10% pack size, rather than the listed 15%.

Scaling to 4 scarabs, it goes to 28% on polished (rather than the 40% expected, and), and 40% on guilded (rather than 60%).

I did not test with Winged scarabs, but there is a potential that those are only giving 12% instead of 25%, assuming the trend above continues. This needs to be still be tested.