Ok I will test.
If the wikis is correct like I suspect taking either has the same affect, taking both spreads the damage
It's just if you take enough troops and the walls are weak enough it may seem like both help.
I made a correction on the wiki.
1：Ranged units(Including Siege Weapons) are also bonused by siege towers.
2: Using both is the best method. They do not weaken each other.