By entering motion hashes into the client these motion hashes are cast in a block each time one block is successfully minted (given global limits are not exceeded).
All (different) motions that are entered (plus custodial votes and park rates) are valid votes.
So you don’t spread anything too thin. There’s no round robin or other distribution of votes going on when minting.
Allowing multiple motion hashes per block in fact was one of the reasons that caused the trouble with this particular vote: the duplicate motion hash check was missing; multiple (duplicate) hashes in a single block counted as multiple votes. That has been corrected with client 0.5.4.