I have a 50% catch when I gang set. I set two sets close together and I get one coon, so that is 50% right. I have never had much luck gang setting for coon around here, we just don't have as many coon as a lot of places. Now for fox that is a little different, I have caught more doubles on fox than I have coons. If I was in Iowa or somewhere with lots of coons I would diffently gang set. Here's a picture of a double pocket gang set I used this season and how it went down.
I left the traps here for four nights and I caught one coon in the pocket on the left and one coon in the pocket on the right the next night and one check I caught a possum in the right pocket. I would surely try gang setting in your location though and see how you do.