As a mass collapses there will be a point in time where the all the matter will be contained by the event horizon but with some matter still coincident with the horizon. If you calculate the density for increasing mass then this density drops as the volume increases.

I was under the impression that once collapse initiates the singularity forms resulting in the subsequent formation of the event horizon. Given the mass of this black hole, there will be a substantial distance created between the singularity and the event horizon. And this is what I'm not understanding about your last post. Are you saying that as the mass of the black hole separates itself from the event horizon, the density of the intervening area is lowered? That would be true if the event horizon had already existed but the event horizon doesn't come into play until the singularity is created. That being the case, the density of the singularity surely increases but I would speculate that the intervening area between the singularity and the event horizon would remain similar to the surrounding environment.

When you say to calculate the density for increasing mass, this density drops as the volume increases. We both understand that the density increases as the mass reaches singularity so what volume are you talking about when you say; " this density drops as the volume increases." Are you speaking of the volume inside the event horizon or the specific volume of the singularity?