as far as I've gathered from datamining FFS, RBS and Wild Ambition, Fatal Fury does have flat levels because the red bar for desperation moves is the point of balance. It would be a little bullshit if Andy got to use a DM before Terry could, especially as you can do them infinitely at half health.
I still have my Fatal Fury Special stuff lying around
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I worked a little in KOF XI and the health values are flat there but I don't have my data anymore
For what it's worth, Vans' KOF conversions use flat 1000, 100