It will be based on SOUR holdings. Helps discourage people from gaming the airdrop by splitting up their tokens and encourages more sales. Equally split drops are usually unannounced.
Still 23 days until the airdrop. You can swap BCH and other coins for SOUR at https://cctip.io or earn some by donating BCH, purchasing from shop using BCH, etc. https://sourtoken.cash