In "Corvette from the Inside" Dave McLellan mentioned that while they were refining the chassis and components etc. that they noticed the difference that angling the radiator had on the radar cross-section.
As Corvette owners were likely to be somewhat 'interested' in having a smaller radar signature they took the decision to angle as many surfaces they could in order to disperse any radar.
As a result they effectively 'stealthed' the C4 in much the same way as the angled surfaces on the F117 Knighthawk were designed to.
Thanks
Dave