The only way I have had luck on coons is to suspend about 4" and try for an elbow catch. I recon their foot must be to small or their stride is one. I don't put bait under the snare. It is two or three foot away with brush on either side to make them go through my trail. A snare is on each entrance. I run this for fox but catch a coon every now and then.
If after a coon a live trap and a honey bun will produce a lot more than a snare. Just camo the trap a little with palmetto leaves or branches on top. Be sure to lock them to a tree, since folks like to walk off with them.