I have a large rain gauge located in an open area which shows more measurable rain than the gauge located on our deck steps does. Mine measures 2 1/4 inches(open area one) and the other gauge measures 1 I/2 inches from the same rain. Why the difference?
If there is also a wind with the rain, that can have a big effect on the amount of rain that will actually make it into a rain gauge. The more open area a gauge is placed in the more inaccurate it will be. The gauge being in an area that helps block the wind but has no blocking above it will likely be the most accurate. In your case it sounds like the opposite is true. This makes me wonder if the one gauge is blocked from above by some trees or something. I have also seen rainstorms that totally dumped on one area and yet an area less than 50 yards away got far less. Just maybe the rain is directed more towards where it will achieve the desired purpose for it, Lord knows!