As far as I remember Usopp's vote is only on Flower and has been since the beginning of the game. So he's not jumping around with his voting pattern at all imo.
Also, you said Queen, Rayborn and Usopp, there must be one scum in between them. So why go back to a Rhea vote and not one of them. Especially why not Usopp when you said that you think he's playing his scum play?