Rail guns destroyed even when out of enemy's range

Hello,

I am playing for about 2 months, but still learning a lot.
Today I had to stop big attack from my enemy: 700 troops, 200 cannons, 10 tanks (more or less).
He was trying to take a couple of week defended provinces (just conquered by my ally) in order to get to my 8 rail guns that were giving him a headache.
When I realized that he could reach and bomb my railguns y moved them back and then managed to stop him in the last city that separated his troops from my rail guns.
The problem is that he has managed to destroy 7 of my railguns, but as you can see in the picture bellow, my remaining rail gun is well out of his artillery range. (my railguns always were together and out of his range).

In the picture he is Libya, I am the Philipines and my ally is India (who still has the same 3 cannons he has had from the beggining of the battle, even if they are in the same position that mine).


I hope you can help me, because I thought my strategy was good (considering his superiority in troops). But loosing those rail guns is an important defeat.

Attached Images