What’s the lip position for zi, ci, si? Are they also “smiling sounds” like ji, qi and xi? Are the lips tense or relaxed when pronouncing zi, ci, si?
Thanks! 
You’re probably looking for feedback from the ChinesePod team, and I’m no expert, but as far as I know the zi, ci and si sounds end abruptly in your throat, while qi, ji and xi get a little more air time. So, I don’t think the shape of your mouth effects the sound as much as it would with other words.