I believe that the estimates provided allow for rates of...

I believe that the estimates provided allow for rates of recovery under different scenario's. So the 400m is not speculated field size but a (P50) mid point estimate of what is expected to be recoverable using standard and proven recovery techniques.  But that's just a number for now.  In reality, and only if successful (CoS is 25%?)....the 'discovered' recoverable resource size will likely (obviously) be within the range between the current P10 and P90 estimates (for recoverable oil).  It could, though statistically unlikely, exceed P10 (as it looks like OEL may have done on their recent discovery) or indeed it may be less than P90 but still be considered a discovery.  Obviously one would hope for something around the mid ranges, or better.

By the way, as seen on this link enhanced oil recovery (EOR or tertiary) gets feilds to up to 60% or more recovered.

All IMO.