How does Morphic Savant work with an Unchained Summoner?

[Amburst]

In the Morphic Savant (http://www.d20pfsrd.com/classes/base-classes/summoner/archetypes/paizo---summoner-archetypes/morphic-savant-summoner-archetype) archetype it says that an unchained summoner's eidolon must have the azata, demon, or protean subtype, and then says than the eidolon has three base forms.
But the with how I understand unchained summoners work, the base forms available is determined by subtype.
Azatas have 2 available base forms.
Demons have all 3.
Proteans only have 1 base form.
Is there something in the physical book I'm not getting because I'm using the pfsrd?

[Psyren]

It's a specific-trumps-general kind of thing. You choose one of those three subtypes, but you get the three listed base forms for your eidolon regardless of which one you picked or how many base forms that subtype normally gets. For example, a Morphic Savant can have a quadruped azata eidolon even though normally this combination isn't allowed, or it can choose serpentine or biped as normal instead.