Aren't the H&R Race springs linear rate and not progressive?
Everything I've ever been able to find indicates that the H&R's are not linear, and that they probably aren't true progressives either.
That leaves a dual-rate design if you look at the spring sitting on the bench at its free length. Basically, the closely spaced coils are
intended to close up at some point so that after that you operate at their high rate. IOW, the closely spaced coils are supposed to contact each other.
The soft rate essentially duplicates the function of a 'tender spring' in "main spring + tender spring" coilover systems. Just that it's all in one spring instead of two separate pieces.
The 'working rate', which is really what you're interested in anyway, is the 'firm' rate and should be essentially linear over at least some of the travel that your driving puts it to (at least on the 'compression' side of suspension movement). You may or may not get the soft rate involved (by extending the suspension far enough to open up the closely spaced coils).
Incidentally, any rubber sleeving intended to prevent metal to metal contact and scuffing actually ends up slightly softening the working rate of the spring. The flip side is that it starts the higher rate a little sooner than would happen with the same spring if the sleeve wasn't present.
Norm