I haven't much experience with a whistle; but I did notice that when I changed between traverse flute and recorder that I had to lighten my tounging for the latter. With the flute I tend to go t-t-t-t-... whereas with the recorder I tend to go d-d-d-d...I think this might be a difference with the whistle and recorder too. The whistle seems to like a nice sharp attack whereas the recorder tone seems to get squashed and even distorted by too strong an attack.

Murray