> Do you think it's the floating ice makes the
> difference? Or is water just unsuitable for this
> procedure?

My guess is that the ice has too much friction with the inside of the glass, especially if there is more ice than there is space for each piece to float freely.

It's possible that different liquids will produce significantly different results. But if anything water would be less viscous than hot chocolate, not more, so I'm sticking with the ice on this one.