What Almeida-Sanchez held is that searches under the border search exemption need to be connected somehow to an actual border crossing, not that they need to occur "at the border". But by the logic of Almeida-Sanchez, the "extended border" is a limiting factor for the government: it suggests that whether or not you've recently crossed, if you're more than 100 miles from the crossing, the border search exception no longer applies.