I was thinking about this. The Sqrt needs to be applied to the total SP for a post and not individual votes. That is,

Sqrt(v1*sp1 + v2*sp2 + v3*sp3...) and not

Sqrt(v1*sp1) + Sqrt(v2*sp2) + Sqrt(v3*sp3)

When it is applied to the total, the splitting of votes doesn't matter to the payout.