[zozbot234]

If free float is 19%, the firm is being weighted at 95% of its market cap, which is 5x the float. If free float is 21%, the firm is weighted at 100%, which is less than 5x the float (that would be 105%). The transition from "5x the float" to "market cap" doesn't increase the weighting any more than the change in float would.

[psvv]

Yes, that's a good point. It doesn't need to cross the 20% to trigger a larger weighting -- it will smoothly increase at a 5:1 ratio below that.