The engine in question here is a .20ci car engine. The squish area is not tapered. I put a rule across it before I filled the combustion chamber in the head. This engine turns over 35k on 20% nitro. I haven't had time to remeasure the engine, but the numbers I got from the second go are 12.72 geo, 9.63 trapped, exhaust closed 82. It's got a 19 degree blowdown.

Effective volume (ports closed) .146971ci
Head + squish = .017023ci
Geometric volume = .199633ci

I'll tear the thing apart and double check the head and squish volume.
The .15 cousin ( same mfg) to this .20 has a geometric ratio of 10.53 and effective ratio 8.79 and exhaust is closed at 75. 17 degree blowdown. I'll post back tomorrow after I double check the .20. I want to make sure I'm accurate.