I had a Fisher Price convertible car seat installed in my EX35 for a few years and never ran into this issue. This car seat was essentially a renamed Britax Marathon, but with fewer bells and whistles. While I preferred installing it with a seatbelt, the LATCH hooks had no problems reaching the anchors in the car.
Which Graco model do you have? Child seats that allow a LATCH installation should have an adjustable length belt. That helps to ensure a tight install since not all cars are the same. It typically gets tightened after engaging the hooks. Also, if you are using a convertible car seat, the belt with the LATCH hooks may have to be routed differently depending on whether it's in front or rear facing mode. If you still can't get the hooks to reach the anchors on the car, you may have an issue with the car seat itself.