This is an example of a set that I typically make for fox. Notice how the holes are only about two inches in diameter on a 45 degree angle (angled toward each other) and about 8 to 12 inches deep. They are not dug, just reamed out with a trapping stake. (All pics can be enlarged.)
Notice how the trap is crowded to the hole. From the center of the trap pan to the holes is about 4 and a half to 5 inches. The holes are about 4 inches center to center. One is for lure, one is for bait. The idea of this set is to make them walk right through it, not work it from the front.
In this picture the trap is already bedded. You can see where the pan of the trap is through the wax paper. Notice the relationship from the pan to the bait hole and the lure hole.
This is what the set looks like after it is finished. See how the set is blended in with its surroundings. When the set is complete, take something (a fox dropping, a small stone, or a small pile of dirt) and set it right up against the loose jaw of the trap. This will force the fox to work the set from left to right and not head on.
Notice where the two trap stakes cross each other. Directly below is where the trap pan is.
This is a view of what the fox sees when working the set. It looks like he has an opening to walk right through. If you want to, you can spray urine on the little pile of dirt, or put lure in one of the holes, or put lure and bait in the holes. This set has always produced for me much better than the regular dirt hole.