I always guessed, but now I looked it up:
The parameters are not stored in the valuetree! The AudioProcessorValueTreeState combines a ValueTree and the list of parameters to make it easy to serialise the state of a plugin/processor. The parameter ends up in an OwnedArray in the processor.
Here is the code:
This makes perfect sense, if you remember, that the actual value of a parameter is not part of the plugin state, because it is depending on the host’s automation.
So there is no need to add a separate pointer to the parameter.
But for all values in the myValueTreeState.state you need to access them from outside the process block.
You can do e.g. as a separate Atomic anything; and update it from a ValueTreeListener… But I usually use them for non time critical stuff, like display settings etc. So there you are outside the audio thread…
