A few rumors got me curious enough to do some tests to see just exactly how much power the ash holds. I never agreed with some people that said using an ash on ixion would be an automatic gold but enough people reported higher than expected rewards after poor performances thanks to deaths or lagg when fighting ixion that I decided to check it out further. My theory going in and still currently is using that the ash at any time even if it does not break the shield adds a significant amount of fate credit and essentially bumps you up a tier from what you would have normally gotten. So bronze>silver or silver>gold. I have never used the ash to break the shield. I normally used it at around 90% on ixion after the fight has started. I have done four tests so far where I am solo in all of them with no chocobo summoned and here are my results:
1: (PLD) Used ash, kept myself alive with a few heals and did a shield lob every 30-ish seconds. Got silver.
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2: (PLD) Used ash, did shield oath + full hate combo only got up to yellow on the hate bar. Got gold.
3: (PLD) No ash, did the exact same thing as #2. Got silver.
4: (Bard) Used ash, died 5 seconds after that, someone rezzed me at around 50%, I did about 15 total attacks before dying again. Got silver.
5: (PLD) No ash, got there late with a friend in a 2 person party. I got 10 hits in and got bronze. She (AST) got 2 hits in after using ash and got silver.
~~~Other people note that it only adds to your own personal credit if you are in a party. One person said that the ash user got gold while the rest of the party all got silver. (credits to cutecookie19 on reddit for that)
This does make sense to me as the ash itself does not seem to generate any hate on its own and fate credit in a party is based on hate generated by all members. I have not done any test or research on this myself though.
So I did finally get to test this (kinda accidentally but it was a decent test all in all). Data point #5 shows me as PLD clearly getting more hate built up than my AST friend where I did not use an ash but she did. I got bronze and she ended up with silver. Obviously the threshold for just getting bronze is registering 1 hit of hate on a fate so the bump up from bronze to silver is simple. I am not a fate expert so I can't say for sure exactly how much you need to do to work your way in to the silver bracket to earn gold with the ash but just being there, alive and in a party should be far more than enough.