I have looked into this known cooling issue a fair bit as the opportunity to "improve" something has always interested me. I have a head that has been modified with 5 extra water take off points to reduce the heat differential around the head combustion chambers. The purpose of this was to reduce the risk of knocking and allow the problems cylinders to as much advance as the other cylinders. The modifications were explored to try and address knock issues on certain cylinders and to see if reducing the chamber ceiling temps of those cylinders would reduce this knock and allow for higher advance to be run. Testing isn't complete but it was clear that reducing the temp at cylinder 6 helped. Turning on your heater (if your race car had one) would have a similar effect. This engineering was not done by myself but I have had a part in it.