This sounds interesting.
Would you like to elaborate on the “threshold concept”? Do you mean the learning threshold? What sort of pedagogy are you assuming with PhD “mentoring” and guidance? I realise that you start with “1.Tell me about your experiences identifying disciplinary areas that your doctoral students often struggle with as they pursue their studies from a distance.” What are the assumptions underlying the struggles? Though I am not doing a PhD, I think such questions may be more resonating with the doctoral students rather than their tutors in the first place. Would the students easily tell the tutor that they are struggling? My experience with my postgraduate studies was: I just enjoyed my study and realised that my professor was there to support. So, the question could be: How would a PhD tutor assesses his/her students – whether he is enjoying or struggling with the study?
Wish you best of luck with your PhD study.
John