I have always heard that objects I.e. other antennas, should be horizontally spaced at least one wave link away from operating antenna. So with that, your concern would be with your CB antenna. At 27MHz you would need about 17 feet of clearance from other objects. GMRS antenna would need around 2 feet. Now how critical this is to radio performace, I have no idea. But if you Google the subject, you’ll find lots of theories