Hi Bill.

Sorry if a simple question gets a complicated answer - but you really hit on the crux of the problem. The simple answer: no, It's not about the angle of the key; it's about how you hold the hand and move the arm. 

To borrow from my own book, you should demonstrate this for yourself.

Hold your arm at your side, with your elbow bent 90 degrees, and your hand out in front of you, palm down, like playing a piano. Now, place the OTHER hand on top of the palm-down hand, and press down - but resist that pressure - don't let the hand be pressed down.

Notice that the muscles of the forearm provide most of the resistance.

Now rotate the palm-down hand palm up, and again, press down with the other hand, resisting the pressure.

Notice that now the biceps, in the upper arm, is engaged and provides the resistance.

This postural change, rotating the forearm, "recruits" different muscles - draws them into readiness, ready to fire. So even though the physical result - a level forearm - is the same, it is a world of difference mechanically.

Interestingly, with the hand rotated halfway to 90 degrees, like shaking hands, the biceps system is still engaged. And it remains engaged with the knuckles at 60 degrees, the "position of function." This is a perfectly natural posture; it is the posture your hands are in when you're walking, swinging your arms at your side.

This is important because when the palm is flat down, the forearm muscles are recruited - ready to flap and flex the fingers and wrist. It is not a coincidence that most (if not all) flat-wristed techniques involve bending the wrist or tapping the fingers. But "wrist flexion," in particular, moving the wrist up and down, is a known ergonomic problem. As is flexing the fingers. There are a HOST of ways this can go wrong. Which includes, as it turns out, forms of glass arm. 

Conversely, with the hand in the position of function, both muscle sets, forearm, and upper arm, are relaxed and available. 

In the technique I use and teach, keying from the position of function is NOT about flexing or moving the fingers or wrist; you don't deliberately "move" the wrist or fingers much, if at all.  Don't misunderstand - they DO move - a lot - but it results from moving the forearm - like the branch of a tree - while the fingers and hand shake, like leaves at the end - following the laws of momentum. I move the branch, and the branch moves the leaves.

It is NOT like playing a piano or typing.

It is more like strumming a guitar.

So, while flat or tilted knuckles seem like a small thing, they have a big impact on technique. 

Of course, as I've said elsewhere - "Everything works." We humans are astonishingly adaptable :-)

73 Chris NW6V