The backing group size on Kusama (and Polkadot) has been set to 5 (configuration->activeConfig->maxValidatorsPerCore). This proposal is aiming at reducing the group size to 3.

Currently, when a parachain produces a block, it requires 2 out of 5 backing validators to verify and sign it in order to back it and move forward. With 2-of-3, we'd guarantee that backing quorum is a group supermajority, so there're not two competing 2/5 backed candidates. And one extra validator is allowed to be slow.
Smaller backing groups should also contribute to distributing the load of approval-checking more evenly.

There's a small risk, however, that with slow/unresponsive validators, parachain slots might be skipped more often with 2/3 instead of 2/5. This should not be an issue in practice since validator groups rotate every minute.

Problem Statement: The current backing group size on Kusama and Polkadot is set to 5, and this proposal aims to reduce the group size to 3.

Significance: Reducing the backing group size to 3 would ensure that the backing quorum is a group supermajority and distribute the load of approval-checking more evenly.

Proposed Solution: Change the backing group size from 5 to 3, allowing for a group supermajority and one extra validator to be slow.

Expected Outcomes: More evenly distributed load of approval-checking and a reduced risk of two competing backed candidates.

#294 Set backing group size to 3

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