system does not handle this correctly. It expects there to be falback and normal images. So you have to trick it to make it work right.
The trick is to set FALLBACK_SIZE=ROM_SIZE
The default config has it set to 0x30000. I suspect it was set that way to allow for the addition of the VGA bios that can't be included in the default distribution.
I tested and for me this builds a 256k image that has the reset vector in the right spot. I don't have any epia hardware so I can't test that it actually still boots though.