Looks like it's the contrary. I made some tests on Warzone 2.3.9 and 3.1.0 by building rows of various things (tank trap, hardcrete wall, machinegun bunker, machinegun tower and heavy machinegun hardpoint) and see in which case the defenses fire or not. The results are rather silly. Not related at all to height as I supposed at first.
These tests were done on flat terrain. Maybe some height can give other results.
On Warzone 2.3.9
- The bunkers can fire through anything but hardcrete wall (hardpoint is still ok
)
- The towers and hardpoints always fire, no matter what is between them and the target
Appart for mixing hardcrete walls with bunkers, you can build forests of everything, they will fire at will.
On Warzone 3.1.0
- The bunkers can fire only through other bunkers (not even tank traps)
- The towers can fire through bunkers and tank traps, but not other towers or hardpoints. They may fire through a hardcrete wall if the target is not hidden at its base
- Same rule for hardpoints, that cannot shoot through tower either.
So bunkers cannot be build behind anything except other bunkers and you can have only one line of tower OR hardpoint, maybe behind a wall but if the ennemy runs close to the wall he will be safe to destroy it (in the case he does not suicide with splash damage

). Works well with a line (or multiple lines) of tank traps.
Anyway, the conclusion of my test is for this topic that "height" don't make a difference between towers and hardpoints