I think the citrus thing is for balancing the pH-- nullifying bitterness & rounding out of flavors. I just got some F'Art citrus mix-- don't kno if its the same as you got, but I'm planning on experimenting w/ it as soon as I free up some time for mixing again.
I'd start off w/ minute amounts till things start to change-- ratios are part of personal preference, experimenting is the way to go. YMMV.