Hi Su,
Good to hear from you.
I'd be more than happy to give you my take on some of the observations you shared.
That
is unusual, since both arpeggios feature "a,m,i".
Answer me this: What is changing? How does the shape change?
It would be great if you could post a video.
Everyone's individual finger lengths vary to some degree, but once you have positioned your right hand in the "sweet spot", i.e. good alignment and no bouncing, all 4 fingers comfortably planted, there is no reason why your hand should change positions to accommodate what is essentially a repeating pattern of identical fingers.
I agree with that.
Are you using a mirror? That would help a lot.
Get a mirror, and position your hand comfortably to alternate "p,i,m,a,m,i" and "a,m,i".
What you're looking for in the mirror is: No change in hand position.
And no change because: The patterns are the same. So, once the hand is in place, the fingers should just be pumping away to play the pattern.
I don't really understand why that would be. One shouldn't be hurting the other.
Both scenarios are not identical, however.
The triplets in Asturias are commonly played p,i,m. I assume that's what you are doing too. So, you're essentially programming the hand in various "p,i,m"
configurations to play the piece notes. (and your hand should be moving across the soundhole accordingly depending on where those notes are, with no bounce or vertical motion.)
That's not really the same thing as playing p,i,m,a,m,i,a,m,i arpeggios repeatedly, with the hand in a stationary position.
Some people also need to tilt the hand slightly when introducing the a finger, because of length differences between i, m, and a, which can sometimes vary a lot among people.
Also, the a finger is typically not as well trained or as dexterous as the i and m fingers, so, that will slow things down a bit, as opposed to just using p,i and m, arguably the most agile.
Just mentioning this to make the point that in your case your hand need not be necessarily positioned the same to play both of these scenarios, i.e. Asturias with p,i,m and arpeggio exercises, in order for both to come out well.
So, in summary, what is not correct:
1) That your hand is changing shape to play "p,i,m,a,m,i" and "a,i,m".
(It looks like you're addressing that).
2) Assuming that your finger/hand placement for Asturias and these arpeggios needs to be identical.
That's not necessarily the case. In both cases though, your hand should be steady, with no bounce, and all fingers should be plucking the strings in essentially the same fashion. As mentioned, that may require some tilting
of the hand to accommodate the a finger, as well as a moderation in tempo to play cleanly if the a finger isn't as coordinated as the others.
These are generalizations of course. You would know best what applies to you. But you might be doing a lot more things correctly than what you are giving yourself credit for.
Incidentally, playing Asturias at a 100bpm clip cleanly is nearing, or at, virtuoso tempo. Kudos to you! So, keep that in mind if that's working well. You must be doing something right. (When I was playing that piece years ago, I never got it near that, cleanly. It wasn't so much the triplets as the fairly demanding left hand work that went along with it. Asturias is, without a doubt, an advanced level piece, and is often played as an encore by the pros, to wow them before they leave the concert hall!
)