Never mind, I did attacking it again and it is fine this time. I guess it was the problem of the AI or the property of this game that units putting the priority to the formation than the full range.
But I wouldn’t delete this topic becuz someone might be giving an reply and would feel unpleasant if he or she finds out that it is deleted, and even this stupidity of mine would be an info for somebody 
My Bombards, without bonuses have a range of 13 with a range upgrade in the Univ. The enemy(Berber) castle in the mission 4(Black Guards?) of El Cid campagin should have a range of 8 and plus 3 with full range upgrades in the blacksmith possibly even tho I didn’t check the enemy castle by clicking it.
But my bombards seem to be attacked by the castle when I directly attack it with right clicking it. Why so??? I don’t know about the range and sight system of the game so I supposed it might be a issue of short sight that doesn’t match the full range. But I checked a wiki and it says the bombards have a sight of 14!!
I don’t understand it. Are there any explanation? Your contribute is very valuable and welcomed by me.