eloquence voices are speaking extra bs

Question

Here below is the code snippet I used to speak some text

  const synth = window.speechSynthesis;
  const utterance = new SpeechSynthesisUtterance(text);
  utterance.voice = selectedVoice;
  synth.speak(utterance);

It works perfectly on Mac Chrome.
But when I try it on IOS Chrome, it behaves differently.

Here is a list of available voice for language en-GB on IOS Chrome.

For voices with compact in the voiceURI, they works fine. They just speak content in text.
For voices with eloquence in the voiceURI, they are speaking extra information, more than the parameter text I gave.
It speaks 'speak. Voice name equals "com apple eloquence en-GB Grandma"'; content in text; 'Voice. speak.'

SpeechSynthesisVoice {voiceURI: "com.apple.eloquence.en-GB.Rocko", name: "Rocko", lang: "en-GB", localService: true, default: true}
1 SpeechSynthesisVoice {voiceURI: "com.apple.eloquence.en-GB.Shelley", name: "Shelley", lang: "en-GB", localService: true, default: true}
2 SpeechSynthesisVoice {voiceURI: "com.apple.voice.compact.en-GB.Daniel", name: "Daniel", lang: "en-GB", localService: true, default: true}
3 SpeechSynthesisVoice {voiceURI: "com.apple.eloquence.en-GB.Grandma", name: "Grandma", lang: "en-GB", localService: true, default: true}
4 SpeechSynthesisVoice {voiceURI: "com.apple.eloquence.en-GB.Grandpa", name: "Grandpa", lang: "en-GB", localService: true, default: true}
5 SpeechSynthesisVoice {voiceURI: "com.apple.eloquence.en-GB.Flo", name: "Flo", lang: "en-GB", localService: true, default: true}
6 SpeechSynthesisVoice {voiceURI: "com.apple.eloquence.en-GB.Eddy", name: "Eddy", lang: "en-GB", localService: true, default: true}
7 SpeechSynthesisVoice {voiceURI: "com.apple.eloquence.en-GB.Reed", name: "Reed", lang: "en-GB", localService: true, default: true}
8 SpeechSynthesisVoice {voiceURI: "com.apple.eloquence.en-GB.Sandy", name: "Sandy", lang: "en-GB", localService: true, default: true}
9 SpeechSynthesisVoice {voiceURI: "com.apple.voice.super-compact.en-GB.Daniel", name: "Daniel", lang: "en-GB", localService: true, default: true}

I am wondering why there are differences in content for different voices.