i'm sure you realise that the group 1 and group 2 chemistry practicals are extremely similar, except for a few compounds. Also, whosoever thinks that group 2 people have higher grade boundaries are wrong. They are usually roughly the same. In fact, if anything, group 1 tends to have higher grade boundaries. In june 2004, group 1 had 75/100, groups 2 and 3 had 74/100. And i remember reading in one other examiners report, forget which, where groups 2 and 3 had 5 marks fewer for an A than group 1.
Just think about what you're saying when you say that groups 2 and 3 will have higher grade boundaries. You are suggesting that the exam board should assume that the students have cheated? If they do that, the honest students will be at a disadvantage.