Attack Wave problem with blocked blocked path (Wall In)

[SledgeHammer]

Greetings!
I am creating a trigger based map, and I send my troops as attack waves.

Now, if the player walls himself in, by blocking the ramp then the waves will just not go on and kill the buildings in between them and the target.

There is probably an easy solution for this, but I havent found it.

I just started editing with GalaxyEditor this week, and I find it very hard to find any good tutorials on triggers.
The only things I find are very basic TD map tutorials.

Regards,
Sledge