Well, I'm not sure, but I would go with the original yardage. If you want it tighter use a smaller needle or a smaller size.There's nothing worse than running out of yarn because you misjudged. I usually get an extra skein just to be on the safe side.
ETA: I just noticed that they are a different gauge. The fixation is a DK weight the suggested yarn is worsted. You'll have to take that into account when knitting it as well. The DK weight will naturally make it smaller unless you do the math or knit a bigger size. Make a gauge swatch for sure.