OED's US pron. of "minion": optional schwa?

[Mark Mandel]

OED online gives the US pronunciation of "minion" (n.1 and adj.) as
/'mInj(@)n/, that is,

    primary-stress   m   cap-I  n  j  left-paren  schwa  right-paren  n

I could understand parenthesizing the schwa

1. in "near" or "square", which are among the examples for optional
schwa after a lax vowel /I E O U/ and before /r/
 (http://dictionary.oed.com/help/pronunciation-3e.html); or

2. between an alveolar stop and a syllabifiable alveolar continuant,
as in "mitten" or "muddle".

But this one doesn't make any sense to me, and the pronunciation key
has nothing about /(@)/ except in context #1.

m a m

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