Unable to adjust the speaking rate for Siri Male or Femal voices on Mac OS

I use the Spoken Content feature a lot on my Mac to read articles and other long-form content. It's a great feature however, I find the default speed a fraction too slow. When I attempt to adjust the speaking rate in the Accessibility Settings via the slider, both the Siri Male and Siri Female voices speak at the exact same 1x speed. The same is not true for the other voices such as Daniel and Oliver. This occurs whether I attempt to adjust the speed in the Settings menu or using the Spoken Content controls on-screen while content is being spoken.

Am I missing something, or is it just not possible to adjust the default speaking speed?

On a separate note, I've noticed a common bug where some words are spoken as if the first letter of the word is separate from the rest of the letters. i.e the word "party" could commonly be pronounced "pee, arty".