I don't see how they could be 152.5 miles away. The position of the Marengo for noon April 15th shown on the map you presented above shows the Marengo was not far from the
Carpathia judging by the distance between the other plots on the map and the position of the Marengo at noon on April 15th. She was south of the wreck, but would still be within a 50 mile radius of the ice field when she saw great refraction at midnight. I believe the reason the refraction grew greater and greater throughout the day and into the night was in correlation to their approach of the huge ice field, and as they came closer and closer, the refraction grew greater and greater. There were a number of icebergs which I understand were dotted to the west and east of the ice field, and a number of them could have skimmed on the northern edge of the gulf stream as they drifted west. The Marengo was too far to see the ice, but not too far to see the atmospheric effects of it.
e.g.
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