@Fernando
Please have a look on how W10 does not recognize correctly SSD Overpositionning.
Partitionning Tools (Mini Tool Partition, AOEMI Partition, MAGICIAN v4.6, etc…) recognizes unallocated space, W10 sometimes ignore it !
I haven’t yet realized any problems of the OS Win10 to detect the overprovisioning part of my SSDs as "unallocated".
I have no idea, why your Win10 Disk Management doesn’t show the unallocated space within your Disk 1.
By the way:
Actually nearly all SSD manufacturers reserve some space of their SSDs for overprovisioning purpose. The user and the OS cannot not see it, because this part of the SSD is hidden. As a consequence I am unsure, if the additional reservation of a certain percentage (ca. 10%) of the available SSD space for overprovisioning is really required.