Yes, speed of approach makes all the difference. Never approach at speeds of more than 10 knots. Your wake glows white in the moonlight and the Japanese were very good at night warfare.
I always flood down to about 30 to 32 feet, the deepest I can be and still run the diesels (I HATE to run on batteries one second longer than I am forced to). Then you can go no faster than 10 knots anyway, so it's impossible to forget
. You'll find you're able to get within 2000 yards surfaced on a good dark night.