If you are trapping in snow country, and constantly having to sweep off your sets to keep them working, it a good idea to set them all the same as this way you will know where the foot target area is. If you are using exposed pans, well, think that one is a no brainer. As far as distance, I raised a couple of coyotes from pups to adult. These guys ran loose around my place from when they were little up until breeding season the next year (then they took off, go figure). I would put a dirt hole in a road side bank and also on the level with a short backing behind it. It seemed they (when they were about 8 months old) would walk up to it and their foot was 8 to 9 inches back from the edge of the hole. Measured this situation a bunch of times and it was pretty consistant. I started using the 9 inches out from the edge of the hole to the center of the pan as a standard and had very few misses.