To be honest I didn't even look at your ranks when I did the estimate. If you are doing alright but a whole lot of people are doing even better, then that's great news because they may pull you up (not worth relying on though). Competition within a cohort is usually indicative of strong academic results.
One example is of my cohort last year: we had 85 Advanced English students, and every year we only get a small handful (3-7) Band 6's. But since our grade was significantly more competitive that previous grades, we ended up having 12+. Similarly, every year we'd get typically 2 Band 6's in Economics. Last year, somehow, we had around 8/48, including a state ranker. Even though this is an anecdote, it goes to show that there really isn't a threshold within a grade for which one can say "yep, the 97 threshold is definitely from this student onwards". Getting 70s in physics and MX1, while there are students in the 90s who will obviously get estimates of 97+, will in no way exclude you from getting 97. Especially since scaling functions can be thought of as being logarithmic in growth; the higher you score, the less your ATAR equivalence rises (or in economics terms, analogous to the law of diminishing returns). So despite you are getting 70% for MX1, you, along with every single student scoring higher than you, are currently within 99+ ATAR equivalence for MX1 (trust me; I checked).
Hope this helps!
