Im assuming you have the spoiler already. Heres what you do, lay it on top and mark the holes w/tape and crumpled paper (so it sticks up from a side view. then, have a buddy place a straw underneeth where you see the impressions. have the hatch half open and look at it from the side. the straw should from an imaginary line right through the hatch to connect w/the taped paper. if both line up from the side view and the distance is comparable on both sides, then there you go. theres other ways to do it but common sense is the best method.