Unfortunately authority 'given' to CBP at the actual border (for crossers) significantly exceeds that of the 100 mile zone. They can basically detain you indefinitely without charging you with a crime and meanwhile strip search you, finger print you, toss you in a cell, etc.
The constitution doesn't apply at the border. Maybe in theory it does, but in reality it doesn't. CBP Officers specifically told me "I consent to whatever happens afterwards when I cross the border."
[ Also been told once, me a US citizen with a passport, that they had decided not to let me in my own country. Was not let through until an HSI detective came to "make sure I wasn't ISIS." ]
You get no attorney. You can't contact anyone. You can't touch your phone, if you have one. You can be tossed in custody without any oversight, and without being mirandarized. I have been booked, finger printed, tossed in a cell as a US citizen who provided a legal passport and violated no laws. You can be tossed in a van, cuffed and shackled and driven wherever they like, including hospitals where they will try to convince doctors to anal probe you (this is a real example from my personal experience).
I've studied the court cases involving US citizens, including a woman who had her orifices brutally penetrated until they were raw by a doctor[0]. THe federal docket shows no real result, and that the CBP investigated themselves and determined they did nothing wrong.
In the end the courts don't give a fuck, and most Americans don't even have a passport. I'm quite sure a good 10% of Americans would go along with a proposal that said "We should allow border patrol to shoot any suspicious persons at our borders." Border and immigration are notoriously dystopian arms of the government, because citizens either have bigger concerns or just don't give a shit what happens there.
If you contact a lawyer regarding border abuse, they will basically refer you to the (swamped) ACLU, because they know it's a waste of their time to even try.
[0] https://storage.courtlistener.com/recap/gov.uscourts.azd.985...