[MikeK]

This discussion is suffering from an 'apples vs. oranges' syndrome.
Two points come to mind:

1) The KB (and certain other new-car pistons) are cast hypereutectic alloy. The expansion rate is significantly less than standard hypoeutectic piston alloys. On the opposite side of the spectrum, forged pistons have a significantly higher expansion coefficient and require more clearance than standard cast alloys.

2) Not everyone uses the same criteria or point to measure clearance. If you look at the KB installation page, HERE you will see their mic point is near the bottom of the tang on the slipper skirts. Those pistons, and all modern new vehicle pistons are cam profiled to an eccentric shape that reduces progressively toward the crown and with a different progression rate in the axis 90 degrees from the pin.

Even if the clearance is ZERO at the designated measure point on some pistons, there is plenty (several thou) clearance if measured higher up and at a different axial point. All well designed modern pistons (not the typical model A junk) also sport reduced land diameters that prevent that area from ever contacting the cylinder wall no matter how hot the piston top gets.

If you were to measure the KB (and many modern) pistons just below the ring lands and above the pin you would find 0.004 or more clearance, usually ~90 degrees from the pin axis, and about 2-3 on the pin axis when the slipper skirt tangs are at the recommended 0.0015-0.0020.

In the 'good old days' of round pistons with full skirts you could just stuff a feeler gauge in the bore next to the piston. You can't do that with cam profiled pistons, either full or slipper (cutback) skirt designs. If you did the results would be disastrous. Apples Vs. Oranges.