Dale,
I use a similar method to your pie plates. After I am sighted in on paper with the load I prefer, I quit shooting paper and just walk the property. Targets of opportunity can be found if one looks. A five gallon pail I have left out is a good target from a variety of distances. And stumps and rocks are usually around. Occassionaly, a groundhog will be present. This way, I have to figure range and holdover. And I try to quickly assume a shootable position. Sitting has gotten to be a bit much for me, (I am 2 belt notches larger than when I was competing) so kneeling and braced offhand get a lot of use. But I am losing weight and sitting will get used more often. Weather also plays into it. Ohio can bring cold and wet conditions and then I prefer to be on my feet, not on my knees or butt!
I have used your pie plate method also but substituted paper plates. Sometimes, I leave them out so they weather a bit and are different shapes and colors when I walk up on them.