According to their link, the error at a human scale is about 1e-6 units on Earth. You need to be doing the math at velocities such that the object's apogee is o

According to their link, the error at a human scale is about 1e-6 units on Earth. You need to be doing the math at velocities such that the object's apogee is over 100k feet / meters from the surface to be "off" by more than 1 unit.