About fan shaped dripper
Fan shaped, Trapezoid, Melitta-style shaped, whichever you like to call it, has been popular since 1930s. People always think of "dark roast and strong tasted" coffee when they see this type of drippers, but is it true?
1. The bottom angle is pretty similar to flat bottom dripper if we see it from the front, but if we see it from the side, the angle is steeper which makes it similar to cone shaped dripper. Plus, the bottom of fan shaped dripper is a rectangle with one to four holes (depends on the brand), so like flat bottom dripper, the water will "get together" in the bottom first, than flow out from the holes. That means your pouring techniques does have effect on the flow rate, but not as much as cone shaped dripper.
2. Fan shaped filter has the largest contact area with dripper wall in three types of filters. For the old fan shaped dripper (like Kalita 102), the ribs and bottom support are quite light, filter stick to the dripper wall tightly, so the airflow within dripper is not running smoothly, which makes the flow rate very slow. That's why people usually use coarser grind size on old fan shaped dripper and always think it makes a "darker and stronger" cup of coffee.
3. Base on the issues of old fan shaped dripper, the manufacturers make some improvements on the ribs, bottom support, and bottom angle, so now we have the new fan shaped dripper (like Kalita Hasami 102 and Cafec G102). The flow rate of these new version is similar or even a bit faster than flat bottom dripper. We can use them to get more floral note and acidity, with a nice level of body.
I think now you already have your own answer for the question at the beginning.
Thanks for reading.