Specs refer to circles, not radius.

TourX wagon 40 feet vs. Sportback hatch 39 feet. Both share the same German Opel platform. What accounts for the difference? Sorry, did not check the respective tire sizes. Could a modification shorten the TourX circle to equal the Sportback'*?

TourX = 235/50R18
Sportback= 225/55R17

I'd bet it'* the tires. Wider tires have a slight natural resistance to tight circles.

1' of turning radius is a tiny difference. Do you need that 2.5% reduction for something specific, or just curious?