Opportunity Influence Analyzer limit number of people in list

We're having some inconsistencies with Opportunity Influence Analyzer in regards to the list of individuals showing up for a given account.

If I select "Last 12 months" as the date criteria, I get a list of 20 people which will differ some from the list that I get if I manually select the last 12 months via Custom.

Some date settings will not show individuals who I know had activity during the dates while showing individuals who had no activity.

Here are my 2 questions:

1. Is the list limited to 20 individuals? If so, can you link to any documentation stating that? (I could not find).
2. How does the tool choose who will appear in the list, if it doesn't seem to be based on activity?