Arch, what you describe is uncommon. Most people hit the 7-PW much easier and have the most trouble with the long irons 3-5. Chances are it's not your feet you need to mess around with. Most likely it's the ball placement in your stance. For the longer irons the ball should be further forward (closer to your lead foot) and progressively move further back (closer to your back foot) the shorter the irons go. Without seeing you swing or the shot result I would imagine you have the ball too far forward on the shorter irons and instead of coming in steep you are almost coming up out of your swing before contact.
Changing your foot position should (SHOULD) be used for when you want to work the ball from left to right (draw/hook) of right to left (fade/slice). A closed stance will promote a draw or hook and the open stance will help fade or slice the ball. Arch, don't get too involved with foot positioning. Set your feet under your shoulders and square yourself to the target line.