Hey there Rob, usually people experience a loss in range when taking steps back to realign their playing.
Occasionally people will discover that the new openness facilitates some higher range.
So consider what you said, “I was owning F’s and now I don’t” to paraphrase. Think about the logistics of that. There was a process that you took to be able to do what you were doing and logic,not to be confused with reality, says if you can do it once you can do every single time. Therefore, something in your process must have changed.
This is where a deep awareness of your playing processes becomes so vitally important. This demonstrates what people struggle with – “why can I do it one day and not the next?” – to which I say – “Well what CAN you do every day?” NOT what can you do when the “conditions are favourable” to steal a quote from Zen in the Art of Archery.
“Do you think this could be an issue with tightening up in the throat?” Again, this comes back to what causes what. How do you tighten the throat? What is causing it? Where does it start? These are questions you must find the answers to by getting out that magnifying glass and going back to mmmmaaaaooooh and discover what is changing.
And to answer your question… NO! You can still squeeze out high F’s with a constricted body. Remember, pitch is determined at the mouth/lips, not the airflow from the body, not the tongue but the lips where contact is made with the instrument.