I agree The explanation given by the OP makes no sense I have sailed these waters many many times If you are off Kanagawa in Sagami Bay then Fuji San is to the northwest and Edo Tokyo is the to north northeast The boats are moving to the southeast towards the coast of the Izu peninsula Because of Fuji Sans height above sea level and the reflectivity of snow you do not have to be due east of the mountain to observe a spectacular sun rise Further confusing the issue the Kanagawa in the title of the print does not refer to Kanagawa Prefecture Kanagawa Prefecture was established in  Prior to that time the easternmost part of what is now Kanagawa Prefecture was known as the Province of  Musashi The westernmost part was known as the province of Sagami The title may refer to an area in Musashi Province near what is now the city of Yokohama The problem with this is that you do not see waves of this size in the confined waters of Tokyo Bay You are only going to see them in Sagami Bay which is consistent with the geography in the print Perhaps Hokusai was exercising artistic license or perhaps he was reinterpreting something he had heard or been told Or perhaps he chose the name because it was more recognizable than some of the other locations he might have used