On Tue, 11 Jul 2017 15:55:30 -0700 (PDT), Quadibloc
wrote:
Since inner planets are always in the same half of the sky as the
Sun from an
Earth-centered perspective,

They don't. Consider e.g Mars and Earth, which both are inner
planets. I think you:re confusing inner planets with inferiör
planets. .

yes, their apparent motion has different properties
than that of outer planets. So their retrogrades will take a
different form.

The only difference is that inferior planets retrograde around
inferior conjunction instead of around opposition.