According to Sirius the 4 second buffer is part of their service, so it wouldn't matter what PNP you have.
From their website:
While we do have in place an extensive network of ground repeaters in many metropolitan areas, factors such as microwaves and physical obstruction (bridges and tunnels) may temporarily disrupt signal reception. This problem is largely held at bay by the four-second buffer created by slight broadcasting delays between our two satellites orbiting over the continental United States. In addition, SIRIUS has in place an extensive ground network of repeaters, which rebroadcast our signal in densely populated areas.
Hope this answers your question Mark!!
From their website:
While we do have in place an extensive network of ground repeaters in many metropolitan areas, factors such as microwaves and physical obstruction (bridges and tunnels) may temporarily disrupt signal reception. This problem is largely held at bay by the four-second buffer created by slight broadcasting delays between our two satellites orbiting over the continental United States. In addition, SIRIUS has in place an extensive ground network of repeaters, which rebroadcast our signal in densely populated areas.
Hope this answers your question Mark!!