The inflation rate currently is at 8.0747% not 9.5% so HP holders get about 1.21% from the inflation. Since the vested hive only accounts for 42.5% of the virtual supply the "interest" earn for holding HP is about 2.84% (people who do not have their coins powered up subsidize those who do stake them).
I am not 100% sure that the virtual supply is taken into consideration for the distribution of the staking rewards but if instead the current supply is the benchmark used then the APR would be ~2.56%.
The 9.5% is some standard number I have been using for a while, although Its old and I know its not exactly correct. I haven't bother with it much, because of the VIRTUAL SUPPLY that you have mentioned above, that is dependent on the stablecoin HBD price, and its getting hard to calculate the exact inflation number, cause it basically changes daily depending on price :)
Overall I agree that 8% is probably closer to the real inflation number than 9.5%.
Also the APR calculation that you point to, taking into account that not all the stake is vested is more exact. Thanks for that.