With peeping creepers installed and the only other mod that affects creepers being Creeper Fireworks the creepers still attempt to breach walls regardless.

Config file used.

Oh, I think I know what might be going on here. If this is the case, I feel dumb for never checking it. I'm guessing creepers no longer check line of sight before exploding when x-ray vision is turned on. So if you're in their normal attack range, they might explode even if there's a wall between you and them.

If you stand a few blocks behind the wall, will creepers still breach that wall? Or do they only do it if you're very close to the wall?