Any combination involving the 4th finger is always a bit tricky, even though if it generally worked well in practice. Often times what goes wrong in concert is not the passage that you particularly practiced!

I like to think of "extending my 4th finger" as a way to give attention. Probably due to nerves, in difficult passages I catch myself grabbing the flute, fingers become tense and thus they curl and become "short". Keep them "long". 

I see playing as an act of releasing air rather than putting out air. One actually needs to build up a certain inner strength to let go. This is especially critical for the upper 2nd to 3rd register, and most indispensable for playing piano in that range.

Try this small but significant difference in mindset the next time you play. Be patient and keep reminding yourself when you notice you're blowing rather than releasing. In the long run, you'll be able to play with much more efficient air management, build up stamina, and be able to have a whole variety in your expressive vocabulary. 

To be able to work with the paradox of tension and release is the key! It's about internalizing, being conscious so that you no longer have to think about it anymore. 

Continuing with the idea of concentrating on the breath rather than the tongue for articulation - practice first without any tongue at all, deep and short "huh". Notice any squeezing in the lips, throat, and HANDS. Ideally, hands should always feel floppy, like just sort of hanging onto the flute. A sign of this is you can feel the vibration of the sound through the hands. I say ideally because it gets difficult during a technical passage, but we just have to keep constantly reminding ourselves.

This is part of a free sound production. 

Then when we use the tongue, experiment whether just using the very tip of the tongue barely touching the edge of the teeth is enough. If it's well-supported and backed up by the air we just practiced, it might be just enough already.

We can think of flute-playing very much like violin-playing (or singing actually, but violin-playing is visually more helpful). There is one place on the string which produces the pitch. Our breath also needs to be at the right place for the desired pitch. We have to train our air so that it arrives at the right place at the right time, along with the corresponding dynamic, sound color, and coordination with articulation.

I think, however, that first and foremost the air has to be at the right place for the note. We play the note not just with our fingers, but the air has to be prepared first. This is very noticeable especially when large leaps involving above the second octave or chromatics happen - if the air wasn't ready for that next position, the note will feel unstable and uncontrollable. It may feel "wobbly", not sitting "right" in the body, intonation problems happen. The fingers were there but the air wasn't there yet, which then causes the embouchure to work unnecessarily and inefficiently. This is against achieving the maximum with the minimum.

Remember, don't play! (here's my explanation of this)

Once this is conscious, other elements are much easier to add on (dynamics, articulation etc.). We train our body to have that "sound position" internalized, just as a string player recalls the correct position on the string.

Play the notes internally with the breath and not with the fingers or lips.