Computing Compression Ratio - check my math?

This is the first time I'm using a dome piston and want to be sure my procedure and math are correct. The engine in question is a .030 over 318 (3.940 bore) and the pistons are KB 399's:

65 - Head CC
2.2 - Deck (piston is .011 in the hole at TDC)
7.1 - Compressed Gasket Volume
1 - Above Top Ring
4.6 - Dome Volume
_____________________
70.7 - Clearance Volume

661.3 - Swept Volume

10.35 - Compression Ratio

I think the above is pretty straight forward, but I want to be sure I measured the dome correctly as my number is different than what KB says it should be.

What I did was install a piston and rod ensuring the dome was completely below the deck. I then cc'ed the block just as you would a cylinder head and got 39 cc's. Then I measured the deck height which was now .218 down. If I calculated that correctly a flat top piston would have netted 43.6 cc's which gives means I've lost 4.6 cc's from the clearance volume due to the dome. The KB catalog says 6 cc's so that's why I am little concerned.