Let's go to something basic: take Terra and put her against Dante. She gets about 30%. Now, add Ryu into the mix, who's about equal to Dante. The voters who voted Terra over Dante must like Terra quite a bit, right? Would the voters who voted Terra like Terra just as much as the voters who voted Dante like Dante? If so, Ryu wouldn't hurt Terra's 30% anymore than he would hurt Dante 70% (proportionally speaking). i.e., if Terra fell to 27%, Dante would fall to 63%.

If not... surely Dante is liked more among those who voted for him than for Terra and her voters. Basically, when Ryu joins in, Terra should get anywhere from 9%-18%. If Terra only got 9% (30%*30%), that would suggest that Terra has relied entirely on dislike (anti-votes) towards Dante and Ryu rather than Terra having any fans... so, a low 9% wouldn't make sense. If Terra got 18% against both Ryu and Dante, her strength is basically entirely her own, and didn't get many "not Dante" votes in the first place. Complicated...

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"Ah, a party! We haven't had one of those. It could be fun! So...what is a party?"
"Well, you drink punch and eat CAKE! ...I think."