Title. Reactive Mending Walls don't trigger their self-repair cloud when hit by worms that are far away, but do trigger when hit by a worm from close range. I did some quick testing in Sandbox mode and it seems to be ~18 tiles, give or take? Walls beyond that don't trigger, projectile splash included (Spit with an aoe that hits both a wall at 18 and 19, it does not trigger the wall at range 19)

Might be intended for all I know. But the range limit is a bit arbitrary.

Self heal effect attack_reaction trigger has range of 18 :-)
I don't know the downsides of increasing it to 60. Need to check.

Lines 92 and 125 in Walls.lua mod file.
Yes, changing values to 65 fixes the title issue, but maybe Veden intentionally set it 18 to motivate usage of other defenses tools or something else.