That means for 20 transactions, single payment 20 times in fee will be 20 times higher. But if I send to 20 addresses at ones, the fee can only increase 3 to 4 times due to the transaction size. This is still lower.
I think you misunderstood me.
Sending 20 single transactions with 1 input / 1 output each, costs 3-4 times more than sending a single transaction with 1 input / 20 outputs.
I get you more and clearly now. Which is the reason I even asked question. I have also gotten that. Thanks.