I just remembered something, in January I also test fit a 18x9 with 5.95" backspace on my car with the 245/40-18 and the fender sat on the edge of the tire. With 3/16" less track width per side it still would not have cleared.
For reference: Here is a picture of a '65 Barracuda (Max's car) where we test fit a 18x8 with a 245/40-18. This wheel has 5.95" backspacing. Not really a good comparison, this is a car with a RMS front suspension. I believe the track on the RMS is 1/8" wider per side than the '73 up disc brake suspension. Max is currently limited to a 225 section width on a 17" wheel because of tie rod clearance, the 18" wheel solves that problem.