Getting back to this subject, because I was using the stock spotting ranges tonight for the sub's watch crew, and sure enough, I became aware of the enemy's presence only when they started firing at me, on a moonlight night, under 10,000 yards.
Anyways, in the tweak file, I see settings for "Visual 1," "Visual 2" and "Visual 3." Within each setting I see two settings, one for "Precise Range' and one for "Max Range." What value should I set for each one, if I want to have my watch crew have a spotting range out to 20,000 meters?