I suspect answering the full question is always preferred, at least for me (I tend to waffle and may ask 2-3 questions in a single voice prompt, and it annoyed me when grok voice recently stopped answering all of them, and instead seemed to select max one to answer with no mention of the others).

Regarding length, I developed the habit of aggressively interrupting, which made voice mode basically perfect. Interrupting had to be learned because it felt very unnatural at first.

Conversely, a skill I'm currently learning is how to ask Grok to 'talk more about X' or 'can you explain that more' (I didn't need to do this prior to 2 weeks ago so I still haven't gotten good at it)