I have a 5.1 system with the center speaker on a shelf above the tv. I am hard of hearing so I need the Center speaker tilted towards my ears while seated. I found these wheel chocks are excellent to achieve the tilt. The ribs on the chocks help stabilize the speaker. I used a laser pointer for aiming. Good luck.
https://m.northerntool.com/shop/tools/product_200594358_200594358