If I remember correctly the X90s was the first model to support uefi booting (not via the network) The x010s were the first models to support network booting in uefi mode.
So a couple of things first for the x010s, while they will pxe boot in uefi mode, iPXE will hang initializing the devices and sit there forever.
So this workaround will with for both the 790 and 7010s.
You can image the machines in bios mode, but switch them back to uefi mode before the first boot into OOBE. The easiest way to do this is to have fog power off the device after imaging. So you will have a tech standing in front to power it on to go into the F2 bios screen and switch the mode to uefi before oobe runs.
The second option is to boot FOS Linux from a usb stick with the hardware in uefi mode. FOS Linux (the OS that is downloaded via iPXE) boots correctly in bios and uefi mode. Since iPXE and pxe booting is not used there is no conflict.
The third option is don’t use 12 year old+ hardware (which isn’t probably an option)