Sounds like you’re measuring the spring uncompressed before installed which mine measure around .530”. The spring is compressed on the clutch when the spring retainer is tightened down. The measurement your checking has nothing to do with the installed height. Install them and you’ll be fine.
Better question: What pressure are they @ installed height?
Same as a valve spring, they ought to all be the same or very similar. That's why you match springs (not for overall length, but for tension at installed height.) We do this on an Intercomp spring tester. You'd be surprised at the variation.
If you don't have a spring tester, you can make your own with a digital postal scale and a drill press.
Yes, installed spring height is the key, and getting a set matched by spring rate checker as well, and theyre relatively inexpensive to replace if you find an oddball or two…bullerbuilt.net has a nice schematic if youre unsure how to measure installed height…