You often ask very broad questions, which are difficult to answer if one cannot see and hear. I will try to answer according to my opinion.
You tell me that you play difficult pieces successfully and also, for example, octave sequences, broken octaves, etc. Well!
Personally, I believe that the position of the fingers and the hand should assume a natural configuration, without forcing oneself to follow restrictive rules or to observe other hands that have different configurations. Rubinstein had a robust and long 5th finger, lucky him, and he had no need at all to think about helping it mentally. And indeed, it is the opinion of great teachers, not just mine, that when we reach a certain mastery, especially in the equality and strength of the fingers, we have actually learned to help, to "compensate" even with the help of the large muscles, the physiognomically weaker fingers. This also involves assuming naturally particular positions. Sandor, in his book, suggests accommodating, for example, a short fifth finger by slightly rotating the hand to make it parallel to the keyboard. All these are more or less theoretical observations and findings which, however, must absolutely not become a "paranoia," as you say.
My teacher, a student of Carlo Zecchi, of Alfredo Casella, and before that of the great Francesco Bajardi, maintained with great conviction that one must listen to the sound, especially in the cantabile, also, as Rubinstein argued with physical examples, by gravitating with great weight on the fingers and "extracting" a beautiful "full and sincere" sound. If we listen to and observe this great pianist, we notice that even his "piano" is voluminous and almost forte, at least with the right hand alone. Casella himself in his book "Il pianoforte" states that one cannot play "legato" without a certain strength. All of this would suggest that there must always exist on the keyboard, note after note, a correct relationship between intensity and duration of sound. And this is the most difficult thing we must achieve on our instrument: the "cantabile legato." By listening and seeking the right sound, the hand will assume a certain position (certainly not outside of a correct "setup" framework) that will be the right one. I know it seems like a reverse process, but, another phrase belonging to Bajardi, the hand (understood in a broad sense, as a complex muscular apparatus) must be a means and not an end.
So after all these words, I take the liberty of exhorting and encouraging you to abandon these unfounded fears, which could precisely focus your attention, even during execution, on the "correct" or "incorrect" position of your hand and reverse the process. We have other things to think about while we play. Therefore: not "correct hand position = right sound" BUT "right sound = correct hand position."
Finally, observe the great Martha Argerich how she handles her hand, with what naturalness... and she did it even as a very virtuoso young pianist! Also observe, in a final video of Brahms' ballads, the great Michelangeli.
Happy Music
