Up until the latest couple of versions of the FAQ/Errata, many terrain tiles and obstacles had specific rules for dealing with large monsters (lava / mud / pits, for example). However, according to the most recent FAQ/Errata I could find, there is a new "rule of thumb" for dealing with large monsters: the "front" tiles of a large monster are affected by terrain/obstacles, while the "back" tiles are not.
I want to make sure I understand this new ruling, especially as it pertains to terrain effects which have specific rulings for large monsters indicating that they normally only affect large monsters that step completely into them.
Now that we have a new ruling, which of the following methods is the correct way to determine which terrain tiles take effect on a large monster passing over them? (Again, assuming that we're talking about lava / mud / pits / ice, and other tiles that only affect large monsters who step completely into them).