Hours on Issues

Hello, I've gone down this rabbit hole before but can't recall the answer. Why can't allocation on hours be adjusted on Issue objects? I have 80 hours planned to this Issue object and each assignee is allocated to 8.3%...not even an even 33.33%. Why is that? Is there a setting I can adjust either on the Issue or in Setup? It is a major problem in my resource planning. Lila Whitney Discover Financial Services