Chef,

My thoughts are as follows:
1. Performing a purely academic exercise on a fixed set of values may not be representative of what happens in real life.
2. Obtaining feedback from the real rigs out there - Peter, MF, your systems - will allow us to set more realistic calculation regime, for comparison.

I'm pretty eager to have more solid feedback from the real-world rigs, before we can proclaim a 'cast-in-stone' result of precisely how COP does vary, in reality. Apologies if this was not they way you wanted to go.