It's amazing what can emerge when you put your thinking cap on: the signs, bays and lines are actually all correct and perfectly match the traffic order, and you interpreted all the signs correctly in the first place (the signs are not best practice as they're missing directional signs, but their positioning makes the extent of the restrictions perfectly clear). It's the parking warden who misunderstood the signs, and I very much suspect that whoever looked at the informal representations didn't bother to look at this properly and just assumed you were parked illegally.
This is going to be really easy:
Dear City of Edinburgh Council,
The alleged contravention did not occur. The signs plainly indicate that the yellow line outside the parking bay is in force on a Saturday, but the single yellow line within the bay is only in force from Monday to Friday. Having checked the map tile at https://drive.google.com/uc?id=15PL0fJFDJkSkKXp_0jvTYMAQyhoywhmo it is clear that this is correctly reflected in the traffic regulation order.
It follows that the bays, signs and yellow line markings are all entirely correct, as was my interpretation of them. It is parking attendant E1720 who misunderstood the restrictions, so it would appear some refresher training would be in order. It is plain that whoever considered my informal representations either didn't understand the evidence, or did not consider it properly or at all and simply assumed I was parked unlawfully, so L Harkness should receive some refresher training as well.
As neither the signs nor the traffic order support the contravention, it would be wholly unreasonable for you to reject this representation.
It follows that should you issue a Notice of Rejection, I will be seeking costs against you at the tribunal.
Yours faithfully,
Send the representation online and get a screenshot of the confirmation screen.
If they don't acknowledge that they got it wrong in the rejection letter, I really think you should pursue a formal complaint against both parking attendant E1720, and against L Harkness: the PCN should not have been issued in the first place, and once challenged it should have been promptly cancelled with no fuss.