The OEM spring free length is 220mm (8.66"), so it matches what you measured. However, this does not mean that your spring is the OEM one, and from the measurements you have provided, it is highly unlikely that it is.
There are about a dozen threads showing above the compression collars on my spring, and I get the correct sag of 3.5" for a weight of 130 lbs. For your weight, I would have expected you to be close to max compression to get the correct sag, but it is exactly the opposite from what you say.
It seems that you need a softer spring; it shouldn't be that difficult to find an OEM one given how many people replace theirs for a stiffer one.