I don't think top prizes should be allowed for not doing what the minigame wants first time. You shouldn't gain the best score if you fail at something. That isn't fair on the better player, and it offers no replay value to someone to make them want to improve.
But there's no replay value this way either - someone isn't going to play the whole game again up to that point just to get a better score at a minigame. Like DynamixDJ said, you're just forcing people to reload from their last save, which makes it pointless to even let them retry without lowering the difficulty. Games are all about practicing and getting better - you shouldn't reward people who get by on talent alone more than someone who worked hard to get as good. In addition, you're rewarding knowledge of this obscure topic - I know what
I'm going to do if I fail it, but if someone who doesn't know and just keeps trying until they get it finds out that they could have gotten a better prize if they'd just kept reloading their save, they are going to be understandably pissed. At the
very least you should make it obvious that if you've failed once, you can't get the best prize anymore.
But it does depend on how the retry works. Does the entire scene restart from scratch, so it's like you never did it in the first place? Or do you get scolded, then get another chance to join a different group of soldiers? If it's the latter, then I can support not getting the best prize, because you screwed up in the continuity of the game. If it's the former though, it makes no logical sense for you to get a worse prize even though you did everything perfectly - if the game world doesn't know you screwed up, it shouldn't penalize you for it (unless you deliberately lowered the difficulty).