I feel that following the taper/contour of the fender is not only more traditional but just better looking. I could see and accent flare at the very bottom of maybe an inch, but than it may be more work than worth. That's going to look really good once your done. Plus it strengthens the fender edge.
I have seen both. One of my friends is deep into Mopars and has a '70 Hemi Cuda that they used what looked like steel drums to make flares/radius. These things were solid! I did my '55 ones and matched the curve mostly. You can see the bend in on the lower rear. The front part is similar.
I just used round stock that I heated in a jig I built and it worked really well. Bending yours might take relief cuts but could be done.
I like a flat edge also, and used very small diameter rod to give my Austin radius strength without a flare at all. But I went with a "factory look" on my Falcon's radius, just because I'd seen a couple done that way, and they looked great. I'm surprised how many people think the radius on my Falcon is stock, until they see another and realize how much it's opened up.