so who's cheating the AQA system?

They're not cheating the system rather they are driving a legal coach and horses through the holes in the moderation process. It's not illegal it's just that the moderation process is seriously flawed: too flawed to give a level playing field to all schools. The sample size is too small for a statistically significant outcome and it's a nonsense that the teachers pick the sample. For a proper moderation there should be a much larger sample which is picked by the moderator according to a formula which will guarantee a representative sample: ie candidatates drawn from the top, bottom, 75th, 50th and 25th percentiles of the ability range according to marks already achieved. A minimum sample size of 20 with a sliding scale for larger cohorts would be somewhere near right.
I have also been moderated by moderators who do not understand the moderation process and do not follow the guidelines issued to moderators by the board. I've never reported them because their lack of rigour has always worked to the advantage of my candidates. I also know that the board will simply close ranks and not admit anything because they are scared stiff of any publicity which will call the board or the system into question. The Daily Mail and it's ilk are waiting to pounce; they would love a juicy story about how stupid drama exams are, especially in the current climate. Leave well alone I say.
Try to get hold of a copy of 'Guidelines for moderators' ; it's issued to all moderators. You can check if your moderator follows them - many don't.
I'll give you another dodge. Do 5 pieces of coursework; give your best candidates their best marks for piece 4. Enter piece 5 for the moderation and slightly undermark. If the moderator agrees the centre's marks then the marks for piece 4 are the marks that count towards the final total. You might even be lucky and get the moderator to raise all your marks then all your candidates benefit.
If it's any consolation the Edexcel system of moderation is even more arbitrary and even more of a statistical nonsense.

 

I have had a variety of group sizes over the years and this year only have 13 which means every pupil has to be moderated as it is now 10 candidates and 6 (or all if less than 6) technical candidates. I have 10 performers and 3 technical consequently all mine will be moderated. I agree it is a flawed system however a few years ago I was berated by my moderator for putting in my lowest group that were so awful it was painful to watch...I was told this was unfair on the candidates and I should not have chosen this group!!!!! and there was me thinking it was about moderating the marks? I have my moderation in 2 weeks and feel apprehensive as it is the first time with the new mark scheme however I don't feel all moderators are not adhering to guidelines (certainly not in my experience)perhaps I have always been 'blessed' with professional moderators even though there have been times I have not agreed with them.

 

Moderation should be a statistical process. According to the 'Guidance for Moderator's', which teachers don't see, both the teacher and the moderator mark the candidates. The teacher should see the moderator's marks immediately after the performance at the same time as the moderator sees the teacher's marks. Haggling is not permitted. The moderator compares the two sets of marks. If the teacher's marks are the same as the moderator's then all is well. There is an allowed tolerance, which I seem to remember, is plus or minus 2. If the marks are outside tolerance by, for example 1 mark, then an adjustment of 1 mark up or down should be made to all the centre's marks within a given range eg the centre was undermarking the top candidates by 1 mark but overmarking the bottom candidates by 2 marks. So, for example, marks below 50% should be lowered by 2 marks and marks above 50% should be raised by 1 mark. The moderator decides on an appropriate cut off point. As I wrote previously the very small sample that AQA uses makes this a very blunt instrument. Maybe that's why the moderators I've come across seem to ignore the guidelines.
When I was a moderator I used raise as many marks as I lowered. There should be no discussion or alteration of marks at moderation. The moderator can explain how they arrived at the marks but they should not change their mind. The adjusted mark is then entered on the mark sheets in that extra column.
Does your moderator do all that? Or do they just say things like ' well everything's OK' or 'your marking's a bit high/low'. I've even seen moderators raise the marks of the moderated sample but not the rest of the candidates; which is very wrong. Not that I complained because they were given maximum marks.