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It is not about how many accounts you have, it is about how much SP you have vested. One account or 1,000. It is the sum total of the SP. One account worth 1,000 SP = 1,000 accounts worth 1 SP each.

All witness votes are SP weighted.

So then you can only vote for 30, is voting for more than say 5 depleting the available vests you give to the original 5?

No, all votes are the same. If you vote for 1 or 30, the vote for the 1st one remains with the same weight.

The difference is that if you have 1000 SP and someone has 1,000,000 SP and vote for different witnesses, the other person will have choice privilege and your votes will matter much less.

Yeah makes sense. So the issue is anyone can technically buy their way to being a witness. The only way to deter that and make it more expensive is if everyone participates in voting / proxies their vote