Click...I squirrel hunt a lot. Some in north central Ohio, (all fox squirrels) and some in West Virginia. (Mostly greys) In my experience, fox squirrels are more deliberate and more bound to trees. I've killed more greys on the ground by far than foxes. Fox squirrels are more of an edge species...they seem to like more open territory.

I've also found that greys sit still less. The biggest difference is the incredible THUD a gigantic fox squirrel will make when you shoot him out at 70'. LOL

I'm sure others have different opinions...but this has been my experience. Good luck!