Well I mark both and would say that any difference between them varies from year to year and is less than the precision with which a maths exam measures how good you are at maths so it is not relevant anyway.
If, as suggested above, the IAL was done by “super clever Asian kids” to get into top universities do you think the universities might, just possibly, have spotted this and adjusted their expectations accordingly? There is certainly little evidence of particular super cleverness in the scripts.