there should be a place in the lobby area that tells how much of the buy-in goes toward the bounty and how much is the bounty per a person knocked out.
You are right, it is annoying not knowing the amount of chips you get after knocking out a player, most of the time the amount of chips you get after knocking out a player is 20% of the buy-in.
It is on the to-do list to make visible the amount of chips you get after knocking out a player.