195F is supposed to be the magic number for tea, which is fairly close the the number for coffee, so the whistle going off somewhat early is a good thing. It just sounds like your whistle is a little premature.
What I know of cooking is that all water will bubble and steam before it reaches the boiling point, due to the bottom layer of the pot, but not the rest of the pot, getting to boil. Full boil is signaled by a "rolling boil," i.e. not just bubbles and steam, but visible currents circulating in the water. Organized, large scale motion takes lots of free energy, and that comes from the generation of serious amounts of steam.
This is not something you can see without severe eye damage in a teapot. Can you say Zojirushi?
