private static Address handleWithExistingProposer(
      final Address prevBlockProposer,
      final Collection<Address> validatorsForRound,
      final ConsensusRoundIdentifier roundIdentifier,
      final boolean changeEachBlock) {
    int indexOffsetFromPrevBlock = roundIdentifier.getRoundNumber();
    if (changeEachBlock) {
      indexOffsetFromPrevBlock += 1;
    }
    return calculateRoundSpecificValidator(
        prevBlockProposer, validatorsForRound, indexOffsetFromPrevBlock);
  }
If the previous Proposer is still a validator - determine what offset should be applied for the
given round - factoring in a proposer change on the new block.
consensus/common/src/main/java/org/hyperledger/besu/consensus/common/bft/blockcreation/BftProposerSelector.java