Does anyone know all or most of the factors that affect the AI in deciding a route to take in conquest?

I've got this cp bunker on a hill that is supposed to be a focal battle point, there is also a tunnel to provide flanking access. Thing is though, the AI completely ignore the hill and all charge through the tunnel. I've already fiddled arround with weight, the path up the hill has a weight of 70 and the tunnel has a weight of 30. IDK what the problem is. The only thing it could be is that the path up the hill is really steep, that doesn't stop the AI from bumping into cliff faces though so I don't see why it would be a problem now...

Check if your planning has anything wrong (ie missing connection, some random barrier ). Also, how much shorter is the tunnel (if it is any)?