Peer-to-Peer Standards Exchange

ASCE 7 (2016 for this question) section 29.4.1 states that for rooftop equipment, one must apply the GCr value of somewhere between 1 and 1.9 depending on the ratio between building area and equipment area. There appears to be no consideration for the shape of the rooftop equipment, whether it is rectangular or round. In many cases, there are exhaust vents which project through a roof surface, like small exhaust stacks. In some cases, round duct runs horizontally parallel to a roof. 

My question is why is there no consideration for the shape of rooftop equipment. If a piece of equipment, or vertical cylinder were mounted on the ground, the shape would have a significant effect on the wind pressure. As seen in Figure 29.4-1 when looking at a square vs round surface, the Cf value with the same h/D value can vary from 1.3 to 0.5 or 2.0 to 0.7. 

Perhaps this question is addressed in another thread which I could not find, but if anybody could provide some background or reasoning here, I would be greatly appreciative.