How often do you bolt the arms directly on the chassis though without some sort of ride height shim? The countersink effect on the arm would only hold true when the arms are directly bolted on. Once you start shimming it the countersink portion comes into contact with the shims not the arm or the spacers in the case of the IRS arms. I'm using the CRC shim set (2 sets actually) on the front of my car to keep a 5mm ride height with 38mm rims on my Mx2. Possibly the holes in the shims are a tad oversized to accomidate the countersink part sticking through.