It doesn't seem to me that the major issue is the distance from the border, but whether there are any reasonable destinations between the checkpoint and the bor

It doesn't seem to me that the major issue is the distance from the border, but whether there are any reasonable destinations between the checkpoint and the border. If there are not, it's reasonable to treat people who pass the checkpoint as if they've crossed the border. It's also reasonable for CBP agents to be able to enforce border-related laws anywhere near the border, subject to the usual law enforcement requirements of reasonable suspicion of a crime based on objective evidence for brief detention, and probable cause for any kind of search. What I find unreasonable is any kind of checkpoint where a substantial number of people passing the point are unlikely to have crossed a border. For example, there's a permanent checkpoint on I10 about 15 miles west of Las Cruces, NM. It's over 30 miles from the border with Mexico in a straight line, and much farther by road. Most people passing this point are traveling between two locations in the US. Everyone is stopped and questioned, and while the questioning is usually not very invasive, it's done with zero individualized suspicion.