Hey Luc,
In general mathematics, the maximum scaled mark if you get 99/100 would be 45.6/50. If you get 70<mark<85 then the scaling factor difference would be 1/50th however if you get less than 70 the scaling factor difference would be 3/50th compared to a mark constant of 90. So basically if you get >85 or above 90, it doesn't make much of a difference however if you get less than 80 it will make a difference of around 4 scaling marks which is a lot and if you get less than 70 it will make difference of around 7 scaling marks which would be devastating to your atar. But the good this is that if you get above 85 there is not much of a atar difference and above 90 means that you wouldnt get scaled down much or not at all however the restraint between the normal mark in advanced mathematics and general mathematics (the subject you are picking), would be concentrated by around 4 scaling marks. Use the atar calculator and compare advanced mathematics and general mathematics by injecting different marks in and find out the differences of scaling.