Actually, that's not the case. The Cabriolets and Speedsters tend to spill the internal noise somewhat better than the coupe - top up or down. I am not saying that the noise in the SAS coupe is very loud - only that the hard top tends to confine the noise much as the greenhouse effect tends to retain heat.
SAS seems to have done a good job on the seal around the top of the engine cover, but I believe it can be improved on. I am anxious to see how Steve addresses the cover on the Jim Kelly turbo coupe.
Since everyone seems to be making YouTube videos, I have been thinking about making one for the coupe, which would address the noise levels at various speeds among other things.