“Hive Power increases at an APR of approximately 3.05%”

I’m pretty sure that the discrepancy between 1.5% and 3.05% is because the nominal 1.5% figure would be actual if all HIVE was powered up. But holders of liquid HIVE get none of that 1.5; it all goes to those who staked. And since slightly less than half of all HIVE is staked, hodlers of HP get slightly more than double of 1.5

Even though I'm not sure how often this 1.5% pays out, it's clearly going up on a regular basis without me doing anything, which is just another reason to stack Hive Power!

I think it’s paid out every 3 seconds (with each block). If you look at the wallet of an account with a huge amount of HP, such as @freedom, and refresh your browser like someone who’s had too much caffeine, you can watch the HP grow:
https://wallet.hive.blog/@freedom/transfers

But remember that vests remain static, even as HP grows.