Well, I must admit I am surprised at some of the sarcastic replies.
Especially when this newsgroup very often contains long threads about
how to calibrate thermometers to within 0.1 degrees for ideal brewing
of rare green teas.

Thank you Warren and Derek, though.

Maybe my post was too long to read and turned a lot of people off, so
here's a quick summary:

When using an infuser basket, is it ideal to have the water level so
high that the entire basket is filled to the brim, or is it simply
enough to make sure that the tea leaves themselves are covered in water
(excluding the ones that float, which will always float no matter how
high the water level is)?

That's the main issue. The space for the leaves to unfurl and be
exposed to water does not change with the water level since that's a
function of the infuser dimensions. The only difference here is that
there isn't that much water *on top* of the leaves -- but so what?
Should that really make a difference?

I'm hoping someone who knows about this sort of stuff will post a
sincere reply. I'll continue to experiment, but it would be nice to
hear some sort of authoritative answer based on science (or something
approaching that).