Vertical Marten Boxes

Many trappers use vertical Marten boxes.  With all of the trappers I know of, the trap is placed in the bottom of the box suspended by 4   1 1/2 to 2" nails, forcing the Marten or Weasel to approach by climbing up the tree or circling the box  (a feat that only nuthatches and woodpeckers can accomplish...ha,ha).  The bait and trap are hidden inside the box.  The whiskey jacks wings would probably hit the sides of the box before it reached the trap 4" inside.   In a recent trapping mag I saw someone has decided to put the trap on top of the box with the bait underneath.  This method could definitely catch non-targeted species.  We have never caught a bird using vertical sets.  We do catch the odd squirrel or fox.  Another plus of these boxes is that the trap is wired to a branch away from the tree and so when the trap goes off it falls away from the tree and is suspended away from other Marten, mice, voles, and weasels.