OK....I think I have figured it out something at least
The meaning of the Zone line seems to be dependent on the value of the Display= line
In the example that CaptainCox gives (for the compass on the nav menu), it has Display=0;No Stretch. This means that the height and with that is included in the Zone line gives the width, height of the compass element, and it renders the third and fourth numbers of the Crop 0= line meaningless (i.e.
0.015625,0.0156252).
Now if you change the Display line to something like Display=2;Linear then things change. The third and fourth numbers of the Crop 0= line now becomes active. For it to display right you need to change those two numbers to 0.087890625,0.205078125....i.e. 90/1024,210/1024. (You would also need to change these two numbers in the other Crop x= lines).
But now the two numbers for the "height and width" in the Zone line can be used to scale this compass element. If you keep the 90 210 the same in the Zone line, then there would be no visible difference in the compass because it is a 1:1 ratio, but if you change the numbers in the Zone line to 45 105, then the compass will be half size (or you can double the size or whatever you want it to be. Basically the change now makes the dimensions of the element (defined in the Crop line) either stretch or shrink to fit the width/height determined in the Zone line.
BTW CaptianCox got your PM, I am going to mess around with the map stuff you are trying to implement to see if I can come up with something.