It depends on the bounty and the number of participants joined in the bounty,as far as I know the longer the bounty the higher earnings you get depending on the ranks and it depends also if the campaign has become successful you will get more higher earnings.
Agreed. Usually with the extension of the bounty, the same increase in payments to the advertising company. The only thing that can make payments lower is the increase in participants due to the fact that the bounty is long and more people join.