Wall Questions

I've been making plans for a new base recently, but I've got some questions before I finalize anything and start reaching for it.
Firstly, I know that there is such a thing as splash damage against similar and weaker walls. From what I was able to gather, a wall with six spaces between itself and another wall of a similar or weaker variety should be safe from splash damage. Is this correct?
Secondly, does the splash only go one wall deep? If I had a layer of brick wall, a layer of plank wall behind it, and then a layer of brick wall on the other side of the plank wall, would the splash from one of the brick walls hit through the plank wall and into the brick? Or would the plank wall take damage, and then upon being destroyed, leave the attacker to face a full strength brick wall again?
Firstly, I know that there is such a thing as splash damage against similar and weaker walls. From what I was able to gather, a wall with six spaces between itself and another wall of a similar or weaker variety should be safe from splash damage. Is this correct?
Secondly, does the splash only go one wall deep? If I had a layer of brick wall, a layer of plank wall behind it, and then a layer of brick wall on the other side of the plank wall, would the splash from one of the brick walls hit through the plank wall and into the brick? Or would the plank wall take damage, and then upon being destroyed, leave the attacker to face a full strength brick wall again?