There's one other Q&A on the topic as well:
B9.54 EX: Bocage: 2nd sentence: Replace "into (but not through)" with "units with Wall Advantage in", because only units with Wall Advantage can be seen through a Bocage hexside from far away, correct?
A. That is certainly a good way to think of this situation.
I have to admit that Perry's answer to my Q&A is the opposite of how I interpreted the rule. The best way I can justify it is to say that units in a Location and the Location itself are treated differently with respect to LOS, similar to how an entrenchment can be seen behind a wall/hedge, but units in that entrenchment may be out of LOS. I would summarize the Bocage LOS rules thusly:
1. A unit behind a Bocage hexside can only be seen from a non-adjacent hex if the unit has WA
2. A Location behind a Bocage hexside can be seen (e.g., an entrenchment within that Location) even from a non-adjacent hex, even though a unit without WA in that Location may be out of LOS.
Part 1 is clearcut to me, and means that Ian's example of dropping WA after Prep Firing to disappear from LOS is valid and a great strategy to use. Part 2 is not how I have interpreted B9.521 before, but again perhaps the entrenchment behind a wall concept makes this somewhat understandable, and based on Perry's answer is how I'll play it from now on.
Again, I'm not sure that this will make a big difference in how you play, since most of the time you'll mainly be worried about whether a unit is in LOS or not and Part 1 above covers that pretty clearly.
Pete