Hi Subtai,
When I spar, my hands are still loose as I described. Let me see of I can paint a picture of how I hold my fist: the thumb is on top of the index finger (similar to the Phoenix Eye, but resting on top), the "face" of my striking area in a Ping Choy are slightly out, with the pinky extended the most (not to say it's full extended) so that each area is gradually going out, with the index finger the tightest when I hit. I don't teach this method to my students as it is something I'm comfortable with and that I've trained for years. I show them how I do it, explain why I do it, and demonstrate how it's beneficial to me. But as you said, most people are more comfortable with the standard fist. It's similar to when you throw a jab, the fist is not tight, but I train to hit that way 99% of the time. And yes, absolutely I can throw it from the chambered position at the waist as that is one of the ways I practice - from a horse stance.
Here're a couple clips where you can somewhat make out my fist shape:
3:34 of the 10 Killing Hands,
3:37 of Iron Wire
That's a good anology about the stone on the rope as that is what I strive to achieve when I practice my punching, especially when working the "internal" punch. As you know, when you've been training this for a while, you develope quirks that work for us that we wouldn't necessarily recommend to others or is "normal"
As for the roll of coins, I use that as an example of how my hands are but without the coins. I know it seems to be counterproductive and counterintuitive to make a fist this way, but like I said, it's something that I've practiced for years and I make it work for me; when I hit someone/something, it is like a stone, not a sponge...
Yui