Reference scale will keep the same line width and get smaller and bigger with the zoom (without reference scale, lines usually keep their line width and only length changes), so I think this is the opposite of what you want. The line is there to represent a physical object from its starting point to its ending point, and as you zoom out those points will appear closer and closer. It sounds like what you're really looking for is the MarkerSymbol behavior, and you should consider highlighting the doors using a marker symbol instead. You might even be able to use both, so when you zoom in far, you use lines to represent the actual door, but when zooming out, using the scale range you switch to a marker symbol that represents the location of the door at the point where the line symbol becomes too small.