I am surprised that no-one has mentioned the thumb hole in relation to the high notes.
This is something that varies from recorder to recorder. When you pinch the thumb hole for the upper register, you need to experiment for a while to find out how much air gap you need to give it to get the best sound as well as be able to hit it straight away whether from a note above or below or jumping up an octave.
For example, my Moeck Rottenburgh alto requires a really tiny air gap for C# and high F.
However my Fehr alto wants a much larger air gap for both notes.
And my Dolmetsch wants a narrow gap for C# and a wider gap for high F!
So, if you experiment with your bernolin, you will find out how it wants to be played. Start by playing the note and adjusting the thumb hole gap listening to the quality and purity of the sound. You may find more than one position for this.
Then try moving up and down with staccato notes trying different thumb hole gaps until it comes smooth. It is important to play staccato since a thumb hole gap that works playing the inverval in staccato will always work with legato but not the other way around.
Then try big intervals.
The cheaper plastics are a little more forgiving than your Bernolin will be, so you will need to practise this until the thumb gap becomes natural.
Once you get this right, you should be able to hit the notes loud or soft.
