The Autopilot interval setting allows a choice of the following distance from 1 (closest) to 5 (farthest). When very slow or stopped, and using Interval 1, move the car closer to the car in front, less than one car length.
To me, the #1 setting provides too much distance when sitting in traffic. I am always astonished at how much distance (2 or 3 car lengths!) some drivers put between themselves and the car in front of them or to the stop line. To me, this is a sure indication of a mind otherwise focused. I earnestly believe that one of the biggest obstacles to full self-driving will be how well the car gets along with other (impatient) drivers. At a stoplight, the car should be tight to the car ahead (2 ft?) and should start to move immediately when the car ahead moves. Otherwise, expect the horn! Finally, if Tesla thinks that a small interval is too short at speed, make the interval speed-dependent or make the #1 setting for in traffic only. I can’t be sure but I swear that when we took delivery of our MS (Dec 2017) the interval was tighter.