Sounds like something you are assuming. If have a source or stat to prove it I would be interested in seeing. Otherwise Im putting it into recylded bin.
You need to make some assumptions to build models to try to understand the game. Otherwise your worldview is shattered when you hear Campbell Graham is on $800k or Kautoga is on $500k. It's possible to make a logical assessment based on known information (the salary cap of $12M, the average salary of $400k and the minimum salary of $140k).
Assuming your bottom 13 players average $160k, that's nearly $10M for your top 17 paid players, which is an average over $450k. If ten of those are on $4M ($400k each) that leaves $6M for the top seven players; an average of more than $850k.
If you don't like these assumptions, make your own salary cap distribution model. But post it here if you're going to shit on everyone else's. I think it's very plausible that Campbell Graham would be on $800k and I've explained how it might work. If you think it's unrealistic, show your logic. Where else could Souths' $12M have gone?