Considering that miners are profit driven actors, the fair share of blocks for a miner is equal to the total amount of blocks the miner would have mined in a blockchain where everyone mines honestly. In fact, a blockchain is in its

optimum state

(no blocks are orphaned) when everyone mines honestly. As result, the gold standard to determine the fair share of blocks for each mining pool is the blockchain where everyone, them included, are mining honestly. Let's call this blockchain in optimum state, standard blockchain. Any blockchain where at least one miner is mining dishonestly, will be in a

suboptimum state