OME is a special case, you can't go by the listed height. Find the chart. It will list coil numbers, and relate each number to an actual load rate. So in essence, Light/Medium/Heavy coils could all give 2" - assuming the vehicles were progressively heavy enough to compress the coils that much. Or, using the same light vehicle, you could get 2"/2.75"/3.5" from the different rate coils that all say 2". Just depends on which coil and your overall vehicle weight.

For instance, I had OME Heavy Duty coils. They were listed as 2", but actually gave me a bit over 3.25" (with a steel bumper and 9500lb winch w/steel cable) Quite a bit more than I expected, and a fairly firm ride because I was rarely loaded down.