I got the 85% used figured out with SATA disabled. Heres my logic.
Before SATA drive connected.
37% used of 160GB = ~60GB used or 100GB available to record so 100/160 = %63 available or 100%-63% = 37% used.
After SATA drive connected with SATA disabled.
Still 100 GB available to record because SATA disabled. But the DVR software is still using both drives combined capacity for total space.
100GB / (160GB + 500GB) = %15 Space left to record or 100% - 15% = 85% used.
So the above explains both of our previous mysterious 85% used when extra drive is attached.
I would argue that this is a PACE bug that the %used is calculated using the total space of a drive that is not allowed to save on.
So I would say that Mediacom is blocking this SATA expansion for sure.