Seems to fit all 3 PAC criteria and yet I'm told it's a root position IAC?

Question

So, as I have been looking for examples of the 3 different types of IAC(Imperfect Authentic Cadence), I run into this:

A cadence that looks like a PAC(Perfect Authentic Cadence) on paper, but which I'm told is actually a root position IAC. How can this be though? I mean these are the PAC criteria:

1. Both the V and I chords are present
2. The bass moves from 5 to 1
3. The soprano ends on the tonic note

And this cadence in Bar 8 of Beethoven's 8th symphony First Movement, as inconclusive as it is because of the textural and dynamic shift, fits all 3 of these criteria, so it should be a PAC according to those criteria. I would expect a root position IAC to not have the highest note of the tonic chord be the tonic note. And yet, that's exactly what happens here, the flute ends on an F. So what, does the shift in texture and dynamics alone make it a root position IAC rather than a PAC? That doesn't make sense. I've seen shifts like that before and it didn't change the cadence type vs if the shift didn't happen, so why should it here? Even considering that it shifts back to a full orchestral forte for a more conclusive PAC in Bar 12, I still don't see why it should make the cadence in Bar 8 a root position IAC when it too fits the PAC criteria.

So is this cadence in Bar 8 actually a root position IAC despite fitting all 3 PAC criteria, simply because of the shift? Or is it just a less conclusive PAC?

Answer 1

Both IAC and PAC are correct, but the IAC interpretation better describes the actual sound of the music.

PAC works, because the score clearly fits the textbook description of such.

IAC works, because the heard sound of the music places the A — doubled in all three of the remaining woodwind parts — at the top of the cadence, with the flute serving a clear background function.

Since the ultimate goal of analysis is to describe the heard effect of the music, IAC is the preferred interpretation.