I just realized this, 6pin PCI-e connectors are only rated for 75W, and you could probably get MAX 200W out of them.
In this blog post: https://hashfast.com/second-tests/ HF says the power consumption for just 2 dies is 300W. Maybe this is why they haven't said anything about running all 4 dies. They are probably running into limitations on how much power they can push through those 2 connectors.