This is simply not how "odds" work.
I think the drop rates were low for a different reason. Each hard node effectively had odds on dropping 4 possible character shards (sometimes 5 if it had a ship on the node) and the drop rates were the same. So I think the coding went something like this (30% chance for a bonus shard to drop, then equal chance to receiving 1 of the 3 bonus characters). If that's the case, the coding was lame. In lieu of double drops, the least they could have done was provide a 30% chance for each bonus shard to drop. Not once did I get a bonus shard for 2 separate characters.