[Update 2]
After adding a 16TB new HDD, the Balancing rules have wonderfull worked, and the replacement rules have been respected.
I had to really further set exclusions file placement rule for other non /MUSIC /PICTURE root structure directories also. It's really wonderfull how this is working. A real state of the art software.
In summary, it was the over 90% usage of other pooled hard drives that forced an Overflow of data, to the SSD.
