All are MBR (FAT32 64 MB + rest NTFS)
Tested also with G4E v2020-12-15 and same thing:
If booting with G2 all VHDs Ramboot fine from it >>> chainloading to G4E all 2.3 GB VHDs fail (same with v2020-12-13 and v2020-12-15).
If booting with G4E all VHDs Ramboot fine from it >>> renamed bootx64_g4d.efi to grubx64_real.efi to test this. (same with v2020-12-13 and v2020-12-15).
But if I boot fron any of both loaders and chainload to the other then the 2.3 GB VHD do not load to Ram.
Same behaviour is present if booting from internal HD, I didn't noticed it before, as I created with BootIce an entry for Grub2 Super UEFI and another for UEFI grub4dos, I was booting from one or the other to test, and just chainloaded to the other to see occasionally the respective menu on screen only, but never tested trying to boot from the second loader, after chainload to it.
By the way I formated the USB FAT-32 partition and by means of UEFI_MULTI all boot files/folders were created again, but this time selected Mint UEFI and I noticed UEFI_MULTI writes fine the info to both menu.lst but it writes to /grub/grub.cfg the line to load/run G4E and it should be done to /boot/grub/grub.cfg, I edited it manually to call G4E from it, and the menu.lst appear on screen but same thing with all 2.3 GB VHDs
If booting with G4E those 2.3 GB VHDs can Ramboot with or without --top parameter, so this means there is enough contiguous Ram to load them below or above 4 GB, tested this when G4E is the second loader trying yo Ramboot the 2.3 GB VHDs and got the not enough Ram message in both cases.
It seems like when one of the loaders runs it is writen on the Ram below 4 GB and the other is writen on the Ram above 4 GB, both in the worst location, as then there is not enought contiguous Ram to load the 2.3 GB VHDs on this PC with 8 GB of Ram. Because the Mini-10-UEFI-WB.vhd of 1.1 GB MBR (FAT32 64 MB + rest NTFS) Ramboots fine from whichever is the second loader, confirming this that the biggest chunk, of free contiguous space available on Ram is smaller than 2.3 GB, on this PC with 8 GB of Ram.