Poor Performance: 2x 980 Pro NVMe (mirrored) write-caching HDDs

[Axiomatic]

The NVMe's are mirrored together in a virtual disk via Windows Storage Spaces for Windows Server 2022. The 4x HDDs are mirrored and striped into a virtual disk and formatted ReFS via Storage Spaces as well. I'm using PrimoCache to have the NVMe virtual disk write-cache for the HDDs to keep them nippy.

Settings are:
Level-1 - 0MB (I don't have a UPS yet)
Level-2 L2Storage 932.51 GB
    -Size: MAX
    -Individual Read/Write Cache Space: Enabled
         -100% Write
    Gather Interval: INSTANT

Block Size: 128KB
Enable Defer-Write: Enabled
    -Write Mode: Native
    -Free Cache on Written: Enabled
Latency: INFINITE (for testing)

Volume Specifications: L1 (Disabled), L2 (Enabled), Defer-Write (Enabled), Prefetch (Disabled)

For some reason, writes to this arrangement will start very fast, then trail off to only 400 MB/s or less. One of these drives will perform at least between 1.5-1.8 GB/s throughout the capacity of the drive, so they're pretty severely underperforming. I don't know if it has something to do with Windows Storage Spaces mirroring or what. But, my cache needs fault tolerance, so I don't know what the deal is there. I'm also pretty sure I have the correct settings for my use-case, so I'm kind of at a loss there as well.

Appreciate any suggestions.

[Support]

INFINITE is wrong. Please see the following page for how to tune defer-write parameters.
https://www.romexsoftware.com/en-us/pri ... write.html

Please note that as long as defer-write is enabled, the risk of using the L2 cache is the same as that of the L1 cache.