I don’t know of any conversion factor, because I don’t think there can be a universal one due to variances between soils’ buffering capacity etc. A sandy soil with low organic matter is going to hold less P than a clayey soil with higher organic matter; therefore when you apply a stronger extractant to the clayey soil it may show much higher differences in extracted P vs. the weaker extractant, whereas in the sandy soil the differences between the extractants percentage-wise will be much less.