The RC is not your typical coupe. It didn't start out life as a sedan nor did it have two doors sheared off in the name of sport. Lexus took the accepted industry protocols and binned them, appropriately so.
So just what did Lexus get up to? Well the under the RC is actually the harmonious existence of 3 distinct platforms. The front clip came from the GS sedan and was chosen for its extra width which was ideal for handling, the middle bit came from the extinct IS C because of its substantial rigidity and short wheelbase, while the rear end from the IS sedan. Mating these three together with something called laser screw welding.
This all sums to a car that is 1.5 inches longer than the IS, yet lower, wider and sporting a 2.7 inch shorter wheelbase.