Ablative DR and Recovery? Help

[satanicway]

The wall advantage, lets me double the efficiency of the wall if i have enough area of effect right?

Lets say, i have enough to make two walls around myself. So the enemy will need to bypass both walls before reaching me, right?

There is any disvantage that only lets you use your barrier in a way that attacks will face only one face of the barrier?
Because i want to add a huge area, to protect mansions of nobles, but it would make the cost too much.
Thats because the rule bases in the fact that adding huge areas to it makes it defend alot better, but not with this limitation.