Bell Potter Report - AVB, page-27

Free float may be calculated using different rules by different financial groups. It relates to the portion tied up with "related parties" (directors / founders / etc) or "substantial holders" who are considered unlikely to be participating in the normal market.

Take a look at the rules for inclusion into the ASX200 - they define free float.

There will be very significant overlap between the top 50 and those who are outside the free float.