Bombers run to find entry points, not bomb walls. Why?

I agree raptelan, first i clean up any buildings in front of the walls,either left or right of the target I'm trying to break throught, then rapidly tap to deploy Al 13 bombers WD to follow them then gunners behind alongside two HG's, don't use juggs in front of bombers big mistake, instead use them as decoys for GP's, for a few seconds anyways, the only time my bombers splitted was when I failed to clean up the area in front of the walls or when I deployed the bombers to close of an opening.