User blog comment:Dudenorz/Brave Burst Levels?/@comment-189.112.73.65-20140203183020/@comment-5007614-20140203233528

I don't think it matters actually... each unit used in the fusion has a chance to boost Brave Burst. I think the best that I've personally seen is +3 levels using 5 units. 2 levels at a time happens more often, but just be prepared to see a lot of zeroes. I think that it gets harder when you get closer to Level 10, but that's just my opinion.