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Legally, any offense that can be written as an NJO "warrants" the maximum punishment under NJP. By that, I simply mean that an NJP can't be reviewed for the punishment level and overturned on that basis. The forum allows for any of the punishments available under that forum. The appeal only goes to the next level commander and while you can certainly argue that maxing it out is harsh, the Brigade commander doesn't have any sort of legal guidance stating that the offense has to match up with a certain level of punishment (there is no handbook out there for commanders stating which levels of punishment should be given for each offense).
If you don't wish to leave this to the battalion and brigade, you have to demand trial by court martial. However, that presents its own issues, because if you lose there, that is a federal conviction and you'd have even greater punishments available. It seems that you have evidence to support your position, but the MP's will get to say their peace too during a trial. You need to be confident of your chance to win and that there can be no legitimate claim against you before I'd recommend demanding trial by court martial.