Theories abound on how water hammer works and how to mitigate it. Basically it is the inertia of mass as per Newton's three laws of motion.
A 3 foot column of water after an arrester should not have much mass or inertia. Most arresters are placed at the wall stops which still have the supply hoses after it.
If you have a very long run and if there are side branches off of it, the inertia could be reflected down the path of least resistance so additional stops on the ends of the branches may help. Hammer arresters normally have a fixed precharge that cannot be changed, so if you have unusually high pressure, that precharge may not be enough and the piston already be near the end of its range of motion. You might want to consider reducing the pressure or use small expansion tanks that can have their precharge adjusted.