I bought a treble recorder thumb rest from Amazon thinking this would help me play the recorder with more ease. However, it doesn't seem to stay in place at all but slides all the way down. It fits at the top of the recorder near the thumb hole, but that's not where my right thumb will be placed. It seems as if the recorder is tapered, being slightly wider at the top than towards the middle. Is that the case with all treble recorders or are there any which are a consistent width/ girth all the way down? If it were the same width as at the top, then it would sit tightly, but since it isn't, it doesn't hold at all and it's my thumb holding up the thumb rest rather than the thumb rest supporting my thumb.