You probably need to top it up with %.
Example: AK
1st boss, 15 tombs
2nd boss, 60tombs
3rd boss, 15 tombs
Why wall gets most tombs? Simple, if someone fishing for last boss, they get only 15. If someone just wanna rage quit, they will think about at least clearing the Wall.
This way, ppl need to at least TRY to complete up to 1/2 the dungoens.
Problem with this is, you will see more "speed runs"