Key-off sample does not follow the decay of the piano sound

That is a correct statement. The Key-Off Sound starts when you either release a Key or you release the Sustain pedal. Next time you are at your acoustic piano listen closely, the Key-Off Sound is to replicate the mechanical noise of the hammer falling back in place and the damper re-engaging the string. It naturally is totally independent of the piano AEG, in that it waits until the Key or pedal is released.

Why, then, in the factory piano presets, does the key off sample decrease in volume if you strike a note forcibly and let it decay somewhat before releasing the key? I don't get an unnaturally loud thunk when doing this with, say, the Natural Grand S6, but I do get it whith this third party sound library. What I'm looking to do is make the key off sample in the third party sound library behave like the key off sample in the Natural Grand S6. Have you listened to the sound clip I gave the link to in my last post?

I can’t help you because I don’t know the sound you are talking about. Rest assured the programming in the Preset sounds is done properly. Contact the maker of the third party library or do a better job of describing what’s going on.

Each Element has its own settings for level and its own AEG.
Sounds like the output level of that Element is simply too loud, you must have edited it, I can’t imagine a programmer leaving that Element that prominent in the mix. Find the KEY OFF Element and mix it to a more appropriate level. If you think this is how the third party programmer left it, take it up with them... but fortunately you can easily adjust it to your liking.

It isn't the initial volume of the key off sample I am looking to ajust. I can do that, no problem. What I am trying to do is get the key off sample to decrease in volume as the sound decays, so when I release the key, I don't get an unnaturally loud key click or mechanical noise. The preset piano and keyboard sounds seem to have this parameter enabled, but my third-party sound library doesn't, and I want to enable this parameter for the third party sound library. I'm sorry if my description seems so unclear. What more information do you need? The trouble is that I don't know the name of the parameter I want to adjust. 🙁

Each Element has its own settings for level and its own AEG.
The parameter you want to adjust is Element Level.

From VOICE mode
Press [EDIT]
Press [1] to view Element 1
Press [F1] OSC
Press [SF1] WAVE

Here you can see Waveform assigned to Element 1 and the XA CONTROL mode
Using the numbered button 1-8 find the Element that has XA CONTROL = Key Off Sound.

Now to adjust its Level... press [F4] AMPLITUDE
Lower the volume til it feels right. It is all about the balance between the Normal and Key Off Sound levels.
Press STORE

You should really listen closely to an acoustic piano, the mechanical noise does not change in volume - in other word, whether you play hard or soft the mechanical noise of the hammers is fairly consistent... it is a detail, that should be “felt” more than it is heard.

If you look in the Full Concert Grand the Key Off Sound Element is set to 40

OK, so the key off sample does not decrease in volume or follow the decay of the waveform. That doesn't alter the fact that there is a difference in the key off sample in the Natural Grand S6 between when I strike a key and release it quickly and when I strike a key, let it decay for about five to 10 seconds, and then release it. I looked at the element level of the key off sample in the Natural Grand S6, and it was at 127. The key off sample is very distinct when I strike a key and release it quickly. However, when I strike a key and wait about ten seconds before releasing it, the key off sample is much less distinct. this seems to occur in the new Clavinet sounds as well. I don't know how or why this happens, but I would like to make it happen in the third party sound library I have. I'm sorry to be so confusing, but I know what I'm hearing, as I'm listening to my keyboard through a high-quality pair of studio headphones. I only wish I knew how to describe it clearly. 🙁