How wide does a 6x6 concrete post footing need to be using an elevated post base anchor?
Well...I had to live and learn. I used 12 inch sonotubes with the same anchor and cheap cement (the fence post kind that was recommended to me)  and 6 x6 posts, which turned out to be a bad idea. 2 of the 4 cement piers cracked part way down where the achor ties were. My solution was to build 21 inch squares around the base about 12 inches down and past the broken areas and leave the rest of the existing footing intact with the more expensive extra strong cement surrounding the existing pier that goes 3 ft down. Hopefully this holds up well..but I am a DIY person so there is trial and error on my end. Get quaility cement and do a wide base to limit lateral breakage IMO. Of course I dont think there would have been and issue if I had not used cheap post hole cement. I am just glad I discovered the issue before the structure became wobbly.