I don't see a lot of value in continuing to argue about this, but I would like you to clarify: you're reading a lot into the difference between "can sense... within 1 mile of you" vs. "within up to 6 miles... within Favored terrain", in both cases explicitly without revealing location. This seems odd to me because "within" and "up to" are actually synonymous, which makes it perfectly natural to just read the phrase as identical to "within 6 miles", but to clarify:
Are you claiming that the text was written this way so that within favored terrain you'd get to pick any radius between 1 and 6 miles, in order to facilitate setting ambushes?
That reading seems problematic to me on two grounds:
1.) Even if you shrink it back down to one mile, one mile is still a large radius, too large to be really actionable for ambushes. "There's a demon... somewhere within a mile of me" is not entirely useless information but it certainly doesn't help you pick a position within that square mile from which to ambush the demon when it arrives. Or are you interpreting it as "within favored terrain, you can choose any radius from zero to six miles, but outside favored terrain it is always exactly one mile"?
2.) You claim that the duration of one minute per spell slot level supports your reading, because the duration allows you to sense the target approaching and then ambush it when it gets there. But even if you use a 5th level spell slot, the ability works for only five minutes, which isn't enough time for the target to cross 6 intervening miles between it and you. Even at 120' per round directly towards you, it moves only 3600' (two thirds of a mile) before the spell runs out, so at any range for which your interpretation allows you to sense distance, the distance never approaches zero before the ability has ended. The duration does nothing to help you plan an ambush under your apparent interpretation--so how can it be supporting evidence for that interpretation?