Fences: Sizes - Positions - Keep Changing

I thought this was the answer to a big problem, but now I find it just adds to the problems. I use this on my PC 24" Monitor, and also on my 55" TV screen. But going from one to the other results in the Fence boxes changing positions, so much so, that I can't find or select some boxes because they are no longer visible on my PC monitor! Or what is there is stretched way off the screen!! I've looked at the answers to other people's similar questions and there really doesn't seem to be a satisfactory answer. What a shame!!