The average bounty allocates the most tokens for Twitter, Facebook, Signature, Youtube and Article campaigns.
is there a bounty that allocates higher tokens to the Signature campaign?
Can't you see the number of participants on this social media campaigns you mentioned? there are usually high numbers of participants on twitter and Facebook than signature, so it is only fair they receive higher allocation so that participants of this campaign won't end up with peanuts as reward,
However, there are very few campaigns that allocate like 40% to signature, sometimes 50% but this are very rare occasions.