There is a line in the rule book that covers what you are looking for.

It states that when a character uses a modified version of a standard power that it still acts like that standard power in all other ways. Perplex modifies combat values by either +1 or -1. Mouth of Sauron uses perplex but he can only modify combat values by -2.

My grammar is not top notch this late in the evening, but the sentence can really be read effectively with or without an "all" in there.

Eradicator's power is a direct statement. Modify his combat values by +1.

Because "combat values" is ambiguous it is not explicitly modifying how many values perplex can modify and so perplex is used normally in all other instances except the value.

Trying saying these two statements to yourself out loud.

"Modify his combat values by +1"

"Perplex can modify combat values."