Julian, yes that is what they usually say, but the cr500 175/50 is a very low profile tyre, and lowers your ride height from say a185 60 048 buy about 20 mm.
Indeed I have seen the top mount mod that you mention done. It would decrese the falling rate of the spring. One of the sprinters,Tony Abbitellio had done it. He was going to do it for me , but I went pushrod instead.
RED 2.0 HPC 230BHP here