Is it tire circumference of revolutions per mile? I would think they would be the same (as a percentage) but when I put my stock size and new size into a calculator I got slightly differing percentages.
https://www.tacomaworld.com/tirecalc
I usually go with a flat 5%. I add 5 miles for every 100 I drive or 1 mile for every 20. I'm not sure .3% makes a huge difference, but if you want absolute accuracy which one would you use?