Why do iPhone and iPad batteries drain differently?

If I charge new iPhone (13 Mini) to 100% and also charge new iPad (11" Pro 2022) to 100%, they both discharge differently. Both devices are kept in Airplane Mode with Wi-Fi radio the only radio on. Both devices have the same settings: location off, background activity off; focus mode do not disturb enabled, etc.

For example:

The iPhone (in standby mode) went from charge of 100% to 88% in 20 hours.

The iPad (in standby mode) went from charge of 100% to 97% in 20 hours.

I have repeated the above experiment multiple times. I have also experimented with 2 different iPads and two different iPhones. Both iPhones discharge significantly faster.

I also noticed that the iPhones charge up quite fast but the iPad charges slowly.

I assume that Apple is purposely running the batteries differently to create these different charge/discharge behaviors. Why does Apple do this?