There's no bonus for getting a high quality synth while making these. It just happened to me (16.5 goldsmithing, could tell it was HQ because of the animation), but you only just get one brass sheet as a result. I think the game is mocking me.
man, i dunno why they make the sheets so easy to make,just use a fire crystal, and an ingot. The only item that dosn't follow this rule (that i know of) is the copper ingot + fire crystal = copper sheet...but i think its' because there's no such thing as a copper sheet (agian, i'm only guessing that a copper sheet dosn't exist)