This plot is super interesting: even though the SBT90.2 outperforms the SFT90 on the upper end, for lower power (<30W) the SFT90 is more efficacious. Since the SFT90 has the same LES (therefore same power density at same drive power) and a smaller footprint (less than half of SBT90.2!), achieving a higher efficacy on the lower end indicates that some substantial improvement has been made, perhaps in the phosphor mixture (which would also explain the reduced tint shift over power) or the underlying die.