Roofs are only a few inches thick
I put the metal plate on the top of the inside of an overhead cabinet
The base of my antenna is only a few inches lower than it would be, if it was outside
Yes the tip of the antenna is pointing down instead of up so the tip is about 23 inches lower
But the radiation pattern is only 12 inches lower than if it was topside/outside
I tested it outside by running the cable thru the window, in my case inside is just as good as outside
Now if you have an antenna to large for your cabinets , that's a different situation
I can explain it to you.
But I Can Not understand it for you !
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1997 F53 Bounder 36s