API 505 and IP 15

I am carrying out a comparative analysis of Point Source Method between API 505 Appendix D and IP 15 section 5.4 and Annex C for a medium pressure (300 psi) and high flow (6000 US gpm) pump.

I worked out my plant area to be Level I.
The pump does have a seal with a throttle bush.
The pump shaft diameter is 100 mm. Base on table C6 my hole size is 0.1SD = 10 mm
The max pump discharge pressure is 300 psia (21 Bara).
Using table C9(a), yields R1 of 21 m for 50 bara release pressure. I have a 2m high barrier wall around the plant area and so I am discounting R2.

I used API 505 appendix D and my R1 is 7.62m (25 feet).

I am concern that the result may be overly conservative by IP 15 because of the release pressure used.
How can there be such a wide gap between API 505 and IP 15? The difference is perhaps in the release pressure. How can I normalize the release pressure to 21 Bara? I do not have the vendor seal leak rates or seal leak hole sizes. Seal Leak Plan is API Plan 65 Standard Single Cartridge type.

I am not able to model the leak rate because I do not have any tool for doing this, even though the process parameters and meteorological data is available.

The question is where can I get the values of R1 for 21 bara release pressure with 10 mm diameter hole? Is there any way the values In table C9 can be normalized? The 2 standards should be close in their results since they are based on the same point source model. Does any body have a different take on the differences in the results?