Non RAID disks show as removable but RAID disks show as normal

Hi everyone!
I researched a lot over this problem, but I cannot figure out how to resolve it.

Motherboard: Intel DP55WB, BIOS version: 0336
BIOS has 3 options for hard drives: IDE, RAID, AHCI

In Windows 10 Pro x64
If I select AHCI in BIOS all disks show as internals, but cannot work with RAID.
If I select RAID in BIOS all RAID disks show as internals, and non RAID disks show as removable.
IRST (Intel Rapid Storage Technology) version: 16.7.0.1009, for Windows 10
1 x SSD Kingston HyperX Savage, as stand-alone, shown as removable.
2 x Toshiba (mechanical) SATA3, as RAID 1, shown as internal.

In Windows 7 Ultimate x64
If I select RAID in BIOS all RAID disks show as internals, and non RAID disks show as internals too.
IRST (Intel Rapid Storage Technology) version: 12.9.0.1001, for Windows 7
This configuration works flawless.

Any advice?
Thanks in advance!

This behavior depends completely on sata/raid controller driver used. For standard intel/ms drivers, you can try this:

- in device manager determine the name of driver service (for example storahci, see the picture)
- if necessary change the service name in the following reg file
- import reg file & restart.

Code:

Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\storahci\Parameters\Device]
"TreatAsInternalPort"=hex(7):30,00,00,00,31,00,00,00,32,00,00,00,33,00,00,00,\
  34,00,00,00,35,00,00,00,36,00,00,00,37,00,00,00,00,00

Or you can check which driver is used in win7 and install/select the same (it may be win7) or similar, but this experimenting is dangerous; before doing this, it is necessary to make system image using macrium - system can crash after disk controller driver change.

Driver: Download Intel® Rapid Storage Technology (RAID) for Intel® Desktop Boards DX58OG, DP55WB, DX58SO2

Thanks muchomurka!
I've already tried that solution with no luck...
I think Windows 10 is not recognizing very well BIOS settings.
As I said, when BIOS is set as AHCI there is no problem at all, but when it is set to RAID then the stand-alone disk is shown as removable.
Strange behaviour...

Windows 10 x64 includes IRST version 15.x.
After reinstalling I just run IRST version 12.9, wich it works fine under Windows 7 x64.
Then problem has gone!
Thanks!