I get that measuring the effectiveness of enforcement is inherently difficult, but isn't the number of arrests made far away from the border an excellent proxy

I get that measuring the effectiveness of enforcement is inherently difficult, but isn't the number of arrests made far away from the border an excellent proxy for how poorly border control is working? You can't isolate yourself from drugs manufactured in-state or from failures of other border patrol units (or successes of drug enforcement away from the border), but you also can't fuck with the stats.