bVI -> I which mode do I treat the bVI

Question

I'm analyzing "Lost in the Woods" from the "Frozen 2" soundtrack and some other similar quirks in progressions and I'm wondering how to treat different modal interchanges.

The Lost in the Woods example:

(the intro)
I IV bVI
I IV

In terms of the bVI do I treat it like I'm borrowing from Phyrigian, Aeolian, or Locrian?

When I played with it a little bit to improvise a solo I went to Aeolian but it occurs to me that the bVI could come from Phyrigian or Locrian as well.

The intro to Under the Bridge does something similar.

D to F#

The difference here is that we have the benefit of a run from the D down to the F# which looks exactly like F#minor until we sound the chord.

How do we treat the F#? Because of the run that sounds like F#minor I tend to treat the D like VI in F#minor then the F# like the I Ionian?

Is this the tendency to swap Ionian and Aeolian as opposed to the other possibilities?

Answer 1

Modal interchange is assumed to be major/minor unless there's a compelling reason to believe otherwise. Given the chord progression I IV bVI I IV, minor would be the clear initial interpretation.