Snaphu unwrapping reference point

I have two questions.

As the first question I looked at the post below.

In the post, you said that the part where the error is likely to be generated is deleted and unwrapping is proceeded. Is this more accurate than including the part with low coherence?

And if I change the value to 0 using bandmath, I wonder if snaphu recognizes it as a nonvalue.
If masking is processed with NaN value, an error appears in unwrapping and the process cannot be performed.

And while using snaphu, I have a question.

We found that the unwrapping result is different depending on how you do the subset on the interferogram.

What is the reference point automatically selected when unwrapping with snaphu?

Can I set this reference point myself?

it is not treated as NoData, but at least phase noise introduces no random patterns inside this area which can distort the result. The latest version of snaphu supports the officially supports masking by low coherence, but this is not implemented in SNAP yet. So you have to run it from the command line and test how well it works. We discussed this here, in case you find a way how to use it and can report: Snaphu unwrapping error - tile issue?

As unwrapping is an iterative process, the results vary between each processing. So even with constant parameters, you might get slight differences. As far as I know snaphu is based on a number of randomly placed starting points and not a single reference point which can be selected by the user. But the snaphu documentation has more information on this.