JohnnyIShootStuff comes through with a good suggestion:

I’ve been doing that for years outdoors as well.  It works great, and you don’t end up with grass and twigs etc. mixed in either.  With the semi-auto rifles off a bench we used to even mess around with propping one side of the tarp up with a chair or cooler to bank the brass off of, and have it roll down right into the bucket.  That was pretty funny when it worked.

Another good thing about the tarp method, it puts a bit of a damper on the efforts of the Brass Bandit.  Although he will still claim that some of the brass is his and it just fell on your tarp because his “ejection is more erratic”.  Whatever bro, keep it all I don’t care haha.