That basically encompasses two thirds of the population.
The last two years have demonstrated a radical need to curtail that range of authority and shift from it being vaguely specified to a concrete legislative specification.
Even ten miles seems (pardon the pun) borderline excessive. There is no reason CBP can't hand off stuff to local, county, state, or federal domestic law enforcement. We have no shortage whatsoever of law enforcement in this country and they're able to communicate inter-agency better than ever via cell phone, tools like slack/teams, text messages, email, and long distance digital radio systems.
Maybe in the 1950's when all they had were shitty radios given them that sort of range was appropriate. Not anymore.
There's a 100 air mile border definition that's material to immigration enforcement (with complicated limitations). It does not determine where searches under the border search exception can occur.