Why is cross firing your mains good, but sub overlap is bad

Sound System Tuning Q A, 3 1. Should I aim my LR line arrays in towards the center to avoid wall reflections 2. Why is crossfiring your mains good, but sub overlap is bad 3. How do you space LR mains Where do you put the mics Pro Audio Workshop: Seeing Sound Here s a link to download the 3 MAPP XT designs I used today