Following that feedback thread to Feedback for v3.1.4 - #220 by aibd we discussed the blur effect expected in the dock.
As said by @irrlicht an exact size image is expected to display correctly. If your image has several feet it sounds like landscape image [1]. In this case Android is expected to display it across multiple screens. (It seems to vary by device whether some advanced image editor is included in the wallpaper setting page seen previously in a Samsung A3.) The blur effect in dock would take care of wandering feet but seems now / again missing on some devices.
[1] Edit but you say the ratio is correct, implies further distortion is introduced perhaps caused by “extra width” of your image is used for horizontal scrolling.
Maybe an opportunity to play with your image on a PC image editor to add a more neutral foreground below the feet (??).