The leverage may indeed change as the account balance gets larger, as when a client has a large amount of funds with us - 500:1 can mean they can open very large exposures which are a risk to both Fusion and themselves if too large.
As a result, when the funds a client holds with us grow, we may begin to reduce the maximum leverage for them - usually in line with the details in this FAQ section, but we may make exceptions on a case by case basis - https://fusionmarkets.com/en/FAQ#Trading%20Questions