This is the privacy screen I intend to have it to block off road noise. I intend to plant another set of evergreen between these Magnolias Little Gem, to get a thick evergreen privacy screen of at least 18 ft.

Another angle of the same set of trees. The second tree from left was also affected with fungus and severe leaf loss. After treatment with liquid copper fungicide and neem oil, these little gem Magnolias have sustained.
And the one on far right is a different type of Magnolia, probably the original one that grows in excess of 30 ft.

Just a thought. Will planting Texas Mountain Laurel (Sophora Secundiflora) be a good idea in between these magnolias?
Or another set of magnolias between the existing ones but a little staggered would do better? Any suggestions?
Thanks

I'm also trying to figure out privacy landscaping for my yard. Someone else might know better about spacing but I do know the Cherry Laurel requires regular watering. Have you considered the Wax Myrtle? 5 ft. growth per year and stops at 20 feet. It is also drought/cold resistant and repels mosquitoes. It's not as pretty though. It would fill in the space between the magnolias. The Mountain Laurel looks nice to me; it just grows more slowly. Also, have you tried mulching to increase the growth rate? I'm also considering the Moonglow Juniper.