Guarani: difficulty pronouncing the vowel y (/ɨ/)

When generating Paraguayan Guarani speech, the vowel y (/ɨ/) sounds incorrect to us. Trying the gn and gui language options has not produced satisfactory results.

This was observed in a custom voice-cloning app using OmniVoice 0.2.1. The app may use Whisper to transcribe the reference, so we have not yet isolated the issue with a manually verified reference transcript.

Could the reference speaker’s accent or the automatic transcription explain this, rather than a model limitation? What reference setup do you recommend for Paraguayan Guarani, especially /ɨ/?

Thanks!