Too little face to face time for blended students?

I've been using interview exams at the end of each unit as an assessment. Well, I like the interviews so much (as both a summative and formative assessment) that I've incorporated them as THE fundamental pedagogical approach of my class (both blended and non blended).

Now, students are required to have brief discussions/interviews with me for every assignment, quiz, or lab that they complete. If they finish an assignment, they bring it to me, and are required to explain it. Then I ask probing follow up questions based on their responses. I carry around my ipad and give a student a grade right there on the spot. I grade students on their ability to convey understanding, but allow them to go back and study and then do another interview another time if they are unhappy with the grade they receive.

This has allowed me to uncover misconceptions held by individual students much quicker and effectively than trying to decipher whether the student understands based on just what they wrote on a piece of paper (quiz, HW, test, etc.). It has also made me concerned with the blended class. I am finding more and more that they have fundamental misconceptions on previous topics we covered compared to the other non-blended students.

I think this may be due to the fact that students who got face to face time with me everyday were constantly subjected to me pointing at their work and asking them "why did you do this?", "when won't this term be negative?", "what does this mean?" and other probing questions about the physics we're learning. The blended students only get this half the time since they meet with me every other day. This might be contributing to them getting to the correct answer on their HW and quizzes without really understanding how.

I hope that using short interviews every step of the way, and only giving credit for demonstrating understanding (rather than just turning stuff in), will convince my blended students that they should seek understanding, not just right answers. And, my real goal is to get the students to the point where they instinctively ask themselves these probing questions to analyze and self correct their own thinking. That type of precise/organized and self corrective thinking, more than any physics principle, is the main thing I want to teach my students.