What's "DNF"? The only thing I can come up with that would be relevant to a race is "did not finish", but that's not even possible in this game (unless someone disconnects in the middle or something, but I'm pretty sure that already eliminates any reward). It sounds like you're talking about coming in last, but since I can't come up with a way to turn that into the "DNF" acronym, I'm not sure if I'm even reading this thread right.

Anyway, I do think how you place in the race should have more than its current trivial effect on your reward. Compare it to the other big draw of the Gold Saucer: In Triple Triad, if you lose, you're out your entire entry fee. If the match ends in a draw, you're out part of your entry fee, though you get a portion of it refunded. (Actually, there I think TT is the one that's off. A draw should result in no change, giving you your entire fee back, but no profit.) Only if you win do you actually receive anything.

For chocobo racing, I think coming in last should result in a forfeit of your entry fee (though your chocobo could still gain some EXP). Coming in seventh should return as much as you spent to enter, but little if anything beyond that. Sixth and above can give enough reward to be a profit beyond refunding what you spent, but with the top three and especially first place being significantly higher than the others.