"and so hit squares are treated as unvisited space squares for deciding if a ship 'could' pass through this square, and then a heavy score weighting is granted to possible locations that pass through a point we know already know contains a hit."
You'll notice that as soon as it wings the ship and knows the orientation that it continues in that direction.
(I concede your point, however, that without this weighting the probability density would be the superposition of all possible locations of the ship independant of other information - that would be a much more complex calculation).
As to how best to place the ships, there is no correct answer, as those who study game theory will tell you. If you had a strategy, then if the opponent knew that there was this strategy, then he could foil you be firing into these locations first, but if you knew that he knew ... etc.