We ride "officials" don't frown on people starting downline of the start area. It's a reality, and in its own way, alleviates congestion in the start area. We could forsee that if the 5BBT were to grow, you might have a few start "zones."
We'd only ask that people joining the ride enroute to stay out of the way while the front "package" --motorcycles, police cars and front riders-- passes. Since many of you have seen this front entourage go by, you probably agree that you'd not want to ride in it, or be overtaken by it.
In my territory of the 5BBT, we "host" a few hundred riders on the Madison Avenue Bridge who fall into the ride a few minutes afther the front package passes.
Checkpoints are at 63rd Street just prior to the left turn onto the ramp to the QB Bridge and at 92nd Street prior to the VZ Bridge entrance.
There is no checkpoint at 56th Street, but here begins the "funneling" to set up the entrance to Central Park. Since you go from +/- 5 lanes road width on 6th Avenue to 1.5 - 1.75 lanes wide on the CP roadway, you need to set this up early to avoid a major (OK, even more major) backup. In addition, at certain major intersections, e.g. 57th Street, we are required to stop the ride for a minute or so to allow cross traffic to pass.