This does not sound right. Maybe venture capital funds work this way? (I wouldn't know about them.)

But with regular hedge funds, you are joining a portfolio and you do get the return even on the positions that were in place at the time you invested. The only differences between investors that may affect the return that is allocated to them are a) their share classes, which may affect investment terms such as fees or withdrawal rights, and b) their respective high watermarks, which may affect the payment of performance fees. Everything else within the same fund will be the same.