So, Duplessy says that while for the deniers parisis of Philip VI there should be some small symbol (dot, star, etc) between PhILLIPPVS and REX, those of Philip IV do not have a symbol between the words. That, and a small difference in nominal weight which is entirely within the range of possible variation between examples (1.274 g vs 1.171 g), are the visible differences pointed out by Duplessy. On the coin here it is hard to see whether there is some symbol before REX. I don't think the form of the letters can be used to tell the two apart. It's weight (1.36 g) would point to Philip VI, if anything.