I agree. I was quite confused with this query - especially since it is designed to calculate a cost based on something acquired on the AD, which is not a static cost at all. As such, xFP can not have an equivalent cost in trading coins, since the item on the AD can be purchased for 9500 coins one day, 54,000 coins another day, and 15,000 another day. Anything purchased on the AD for trading coins is in constant flux completely dependent on what group of people have access to it and choose to attempt to bid on it. And any attempt at a bidding war will usually artificially increase the cost.
Example, I bought all 7 Selection Kits for Pillar of Heroes for less than 2000 each (I refused to pay more than that) - but I have seen those exact same kits recently selling sometimes in excess of 20,000. You cannot create a 'reasonable exchange rate' based upon the currency of something that is in such extreme flux.