Board Thread:Fun and Games/@comment-26208943-20150313025712/@comment-25563656-20150313052830

Stevonnie also has two arms. It could be that Garnet and Stevonnie have higher levels of harmony than the other fusions that we have seen. Therefore, Garnet and Stevonnie are more capable of controlling the form that they take.

In other words:

Super-large with "extra" Arms = Tons of Power and Less Precision

roughly 6.5 ft tall with two arms = Adequate amount of power and Tons of Precison