Laptop BIOS has ReBAR enabled, yet Linux detects no ReBAR!

[Aqua1ung]

ArchLinux user on Thunderbolt 4 Raptor Lake LG Gram laptop, with Razer Core X V2 Thunderbolt enclosure hosting ARC B580 or RX 9060XT eGPUs. My UEFI/BIOS has all the requisite ReBAR switches enabled (be it by default or not):

1. ReBAR enabled (default)
2. Above 4GB MMIO BIOS assignment = Enabled (default)
3. OS Native Resource Balance = Enabled (not default)
4. ITBT Root Port 1 Configuration/Reserved PMemory = 4096, PMemory Alignment = 31 (not default)
5. ITBT Root Port 2 Configuration/Reserved PMemory = 4096, PMemory Alignment = 31 (not default)

Yet Linux does NOT detect ReBAR! My investigations reveal that there's some negotiation happening at eGPU connect time, whereby the eGPU requests a 16G BAR, and can't get it, so the system defaults to a 256M BAR, which is tantamount to no ReBAR.

Question is: will I in any way benefit from ReBarUEFI? Should I even bother messing with it?