It depends - do you have a base elise and you weigh little (best clearance) or do you have the lower ride height from the optional suspension and you weigh a lot. When loading my elise, I even found the Difflow diffuser to be the limiting factor, not the front lip.
Because of all the variables, set some weights in the car (or two people), and grab a yardstick. Measure the approach and departure angles, add in some margin, and go from there. If you have the contractor present, he can help and make sure the measurement is something he can work with.