I don't think it's gonna matter much. When I bought my SCP exhaust system, it included downtubes with high flow cats. One of the cats was welded onto the downtube upside down with the sheild facing the road surface. I didn't notice it until after the exhaust system was already installed.
I drove it that way for 3 or 4 years. The sheild eventually fell off because it would collect and hold water when going through a car wash and the spot welds rusted out. Probably better if it's on there, but IMO it's not going to cause a problem to run the car without it.
David