What are the Center and the left/right flanks in a Dragonfire army?

Your army lines up on 3 positions: Left Flank, Center, Right Flank. That's where your 3 dragons go.

The Center is special: it's the aura hub. The aura of the dragon standing there spreads across the whole line, meaning the entire army. The flanks are mostly there to hit.

The direct consequence for building an army: put the dragon whose aura is most worth spreading at the Center — a Champion by default, since they have the best auras on average; a Warrior if you want to push Initiative. Your biggest hitters go on the flanks.

Don't waste the Center on a plain bruiser: it's your team multiplier.