When crows are in a field sitting on the ground, they are feeding. Use a feeding call sound! This type sound brings crows to your decoys with a casual, nonchalant, careless disposition.
Do not be in a hurry to switch to a fighting, or distress call either, in a feeding situation, after you fire a few shots. This may bring many crows to your setup at once, and a bunch of them may see you. What I have found best in a feeding set up, is to try to get only a few crows to commit to your setup at one time, allowing you more time to pick your shots without mass confusion of a dozen or more crows over you all at once.
I have a feeding sound in my Foxpro FX-3, and I have killed more crows with it than all other call sounds combine. Of course, I almost always hunt in feeding fields. More productive for me than run and gun. Takes a lot less energy too!
Arrange your decoys in the same manner that you see live crows in a feeding field. Put the closest one about 15 yards in front of your blind, and the further ones about 30 yards from your blind. Use 7.5 or 8 shot, and don't pay any attention to anyone who tells you to use No. 4,5,6 size shot. If you don't think small shot will crows effectively, ask Bob Aronsohn what he uses.
I found out on Saturday that my FoxPro sound called "CROW PARTY" and "CROW GATHERING" was our best. Isaac also had a different CROW GATHERING than mine on his Alpha Dog that we played at the same time. Both worked great.