the cwr cannons are set to calculate their shots... gather a firing solution as to why sometimes they shoot the terrain in front of them well i do not know. though I would suggest not placing them behind a hill... for cannon that have to shoot through a hill are not exactly ideal
if one does not learn from the failings of the past they are likely to suffer its return.
Might just as easily be a mismatch between the invisible terrain map that the game mechanics see when doing the math on projectiles and the visible terrain that the player sees.