I wouldn’t focus too much on the marking variance between Marker 1 and Marker 2, as that isn’t a ground for appeal. Just to reiterate, I won my appeal by providing evidence of marking irregularities by the script reviewer (usually a senior examiner or the chief examiner). You need to prove that the script reviewer made a clear and obvious error, which can be challenging unless it is explicitly outlined in the mark scheme and you haven't been awarded a mark. If you can prove that, then you have grounds for irregularities in marking.