You are right. I need to revisit that. I might need to extend that timeout. I have seen these specific sensors work over 2m (to a flat wall).
Haven't seen cross-talk in my testing yet, but I haven't done anything too stressing. This is for a large robot, so the sensors will be about 20-50 cm apart, more or less radially pointing outward.
For collision avoidance I am hoping that a false positive from a simultaneous ping would not necessarily be a bad thing. If I receive my neighbor's ping from a tilted surface nearby (which I still need to avoid), that is better than not seeing anything. I hope that the first echo sensed causes the pin to go low, and I get the "conservative" estimate of distance to a nearby obstacle.