$\ce{Co^3+(aq) + e- → Co^2+(aq)}$ +1.81 V

$\ce{Mn^3+(aq) + e- → Mn^2+(aq)}$ +1.51 V

This is the data of Standard reducing potentials I have found on internet. Why is reducing potential of $\ce{Mn^3+}$ is less than that of $\ce{Co^3+}$. $\ce{Mn^3+}$ converts to $\ce{Mn^2+}$ which is half filled configuration and hence more stable. Am I missing something?

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    $\begingroup$ The answer is simple, you are overlooking the most important trend in the 3d block. Everybody likes to think about the fancy stuff like exchange energy, Jahn-Teller effects, blah blah blah but they forget that effective nuclear charge increases going across the 3d block. $\endgroup$ – orthocresol Mar 22 '16 at 23:30