Hi Philipp,
Thanks for your response. Yeah I actually figured that out after looking looking at the netcfg code and seeing the "01-" being purposefully excluded from the address capture. So then I looked up the specification for PXELINUX and saw the hardware type at the start.
So, I've just hardcoded (eww) a "01-" before the ${netX/mac} in the iPXE config.
Thanks for the answer! And sorry for not updating this sooner. This can probably be closed as a non-issue, but not sure if it's worth while adding a comment to the code, or something.