Hey Torq,
Good question: - The setting is subjective but pretty intuitive after you use the chart for awhile. Linear regression is about defining the trend. Once the trend changes, the setting has to change. Of course, there are trends within trends, and the strongest points are when L/R lines from various trends meet.
Of course, the longer you can "justifiably" define the trend, the more powerful the L/R lines become.
Once you get comfortable with the "art" of it, you'll find it a very powerful tool.
Walking Shadow introduced this tool to me last year and has a strong understanding of it.
P.S. The different setting you've seen on my charts are from measuring differing indeces. (i.e. the trend durations differ)
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