It folds three different things together: how completely the displacing fluid pushes oil out of a pore it enters, what fraction of the reservoir that fluid actually enters, and the rate at which the well becomes uneconomic. A recovery factor borrowed from an analogue field is only as good as the analogy.
Solution-gas drive commonly leaves most of the oil behind. A waterflood raises the fraction by holding pressure and sweeping more of the rock. The residual oil saturation is the oil left inside swept rock; the recovery factor is smaller again wherever the sweep missed.