Something else worth considering, if you're seriously concerned about EDTO fuel reserves. The CP calculations, at least where I work, are on a pure straight-line basis. There's no allowance for doing a 180, and no consideration of whether there might be a 20000' mountain range between CP and the adequate airport. So what you think is enough, may well not be. Also the required reserves are very low - can you imagine turning up at Biak in the middle of the night, engine out, with only 15 minutes and approach fuel?
On the other hand: this is really a risk-mitigation exercise against a very low-probabiity failure. We're required to have EDTO CP fuel before departure, but once airborne, it's no longer a requirement. While I agree that we should always have enough fuel to get safely to an airport regardless of what happens, the fact is that we don't. It's just that the things we don't allow for are of extremely low probablity. I'd suggest that a depressurisation exactly at CP is also a very low probabliity. If you're aready operating in accordance with CARs and your company's SOPs, do you need to insist on covering that very low probability? That's up to you, but think about this scenario:
You're operating Sydney-Honolulu with 300 pax. The destination weather is fine, and there's a contigency build-up for CP, so the result is that the plan has you arriving in HNL with stacks of fuel - let's say 1.5 hrs on top of normal reserves.
Enroute, all is going pretty well. The destination weather is still great, and there's nothing the matter with the jet, but you see that you'll be 200 kg short of the flight plan contigency fuel at CP. You are, of course, completely legal to continue to HNL, and the chances of a depressurisation happening at exactly CP are tiny. So, do you continue legally to HNL, or do you take your serviceable jet and its 300 pax to Cassidy (Christmas Island)? How do you see the subsequent discussion with the Chief Pilot going if you choose to divert?
Not trying to tell you what you should or shouldn't do, just throwing it out there for consideration.
