All the WK2 OEMs, whether the be 18s, 17s, or 20s, have the same overall tire diameter because they all use different aspect ratio tires. The 20 inch has bigger wheels but less tire side wall, the 17 inch wheels have less wheel but more side wall. The tire diameter comes out the same in each case (a 20 inch wheel plus 10.5 inch in sidewall is the same overall diameter as a 17 inch wheel plus 13.5 inch in sidewall which is the same overall diameter as a 18 inch wheel with 12.5 in sidewalls.). Depending on the tire, a 22 inch wheel could have a much smaller diameter than an 18 inch wheel.
Because all OEM wheels/tires have the same overall diameter, the star scan tool may not provide the tech with WK2 tire factor adjustments. Other chrysler vehicles have a wider variety of tire sizes but the tool only lets the dealer pick one of the optional sizes. Clever techs discovered some work arounds, but those may not work here.