A subject many seem to have varying opinions on !
Speaking to one who set the overbook factors, by judgement, they said the worst on the BA network were evening UK to India, where you could be 50 (or even more) over, and still get away with everyone accommodated and not a spare seat. Result !
Denied Boarding Compensation amounts in the calculation should be factored by what proportion of such pax actually receive such a claim, figures as low as 25% are common. I know we here are well informed about it, but not all are, particularly if there is a convoluted reclaim process. I gave up on one with Air France after a year ("must refund to the original credit card", "must refund through travel agent who did booking", etc).
OB's are not wholly down to no-shows. For example, a factor on last of the day short hauls is passengers on full fare tickets turning up early and being transferred forward to an earlier flight, having booked the last of the day as an insurance in case their meeting drag on that long. So you OB the final flight based on normal numbers of this, but can get caught once in a while.
OpUps can of course only happen if there is still accommodation in the premium cabins, and there may be an issue with premium catering numbers already being loaded.
Routine denied boarding however really shows you have the wrong model. The US carriers for some reason seem to be poorer at it than most, I don't know how their algorithms can be so wrong.