PREMiso Earth's model

Hi guys,

I have a question/doubt regarding the Earth model used to compute the Instaseis database I am using.
I am using the PREMiso database with a dominant period of 2s.

I extracted the Earth's model PREMiso from Axisem -- I am assuming that the database is computed with this model, am I right? -- and I noticed that it does not have the low-Q zone between 80 and 220 km that is part of PREM. Q in this depth range is 80 in PREM, but 600 in the Axisem PREMiso model.
Has this been done for a specific purpose?

Thanks,
Lucia