@AndrewC The menu entries look perfectly sound to me.
I would ask you to try this exact configuration on any machine you can get your hands on that is capable of UEFI mode (not mixed mode, turn that off). If it flat-fails across the board (which I doubt), that’s one thing. But if it works on any at all, then it’s likely something to do with the hardware or with the boot ROM ipxe.efi.
That error from your first post “Could not boot: Result too large” really sounds like it’s boot ROM related, or a hardware issue.
It could be resolved as simply as trying different .efi files. Your options to try are on your FOG server in /tftpboot. Just change your DHCP UEFI policy’s option 067 to a different file name, try them one at a time. Do a complete power-off on the computer you’re trying to boot with for each try.