965 Deck Height

[jacksd3]

Since my '92' pistons are flatops I used the simple method of measuring deck height using a vernier caliper. I came up with about .5mm for each of the cylinders. The aluminum ring that goes between the head and the cylinder is about another .48mm. So it would seem like I'm well short of the 1.25 - 1.5mm standard. My cylinders use the 964 o-ring at the base of the cylinder so I can't gain anything there. What am I missing?

Thanks in advance!