How to set up a dual SSD Fusion Drive?

I own a 27-inch late 2012 iMac. The HDD in my 3 TB Fusion Drive has died, so I replaced it with a 2 TB SATA-SSD. Since the 128 GB M.2 Apple SSD is probably still a lot faster than the new SSD, I wanted the two drives to operate in "fusion mode" once again, rather than have two separate volumes.

Using diskutil, I unmounted the Fusion Drive, erased each of the physical disks, created a new CoreStorage Fusion Group (diskutil cs create "Macintosh HD" disk0 disk1) and then a CoreStorage Fusion volume (diskutil cs createVolume "Macintosh HD" JHFS+ "Macintosh HD" 100%). I then installed macOS High Sierra with no issues and migrated my data from a Time Machine backup. Everything appeared to be just fine until I arrived at installing Windows: Boot Camp would only let me use 110 GB for the new partition despite one TB of free disk space.

Another look at the drive configuration revealed that something has gone terribly wrong after all:

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *121.3 GB disk0

1: EFI EFI 209.7 MB disk0s1

2: Apple_CoreStorage Macintosh HD 24.5 GB disk0s2

3: Apple_Boot Recovery HD 650.0 MB disk0s3

4: Microsoft Basic Data BOOTCAMP 96.0 GB disk0s4

/dev/disk1 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *2.0 TB disk1

1: EFI EFI 209.7 MB disk1s1

2: Apple_CoreStorage Macintosh HD 2.0 TB disk1s2

3: Apple_Boot Boot OS X 134.2 MB disk1s3

/dev/disk2 (internal, virtual):

#: TYPE NAME SIZE IDENTIFIER

0: Apple_HFS Macintosh HD +2.0 TB disk2

Logical Volume on disk0s2, disk1s2

EAC5E1EA-BD4E-4295-992D-807629B3BECC

Unencrypted

The Boot Camp partition has been created on the Apple SSD while the SATA SSD appears to be the boot volume! Windows located on the Apple SSD is particularly unexpected since with the original configuration, Boot Camp could only access the HDD portion of the Fusion Drive.

Starting over from scratch, how can I create a Fusion Drive with the two SSDs that behaves like it is supposed to?

• macOS and frequently used files are stored on (or dynamically moved to) the Apple SSD.
• All other files and the Boot Camp partition go to the SATA SSD (just like they did before with the HDD).

Thank you!