There is an industry standard of concaving 11 degrees, although its hard to find why that is so, the only reference I could find was someone believed it was the angle found to be best by the the American military?

I have tried a barrel end machined at a 45 degree convex (as I take the crown as the very edge where the barrel bore ends) I was actually doing it go give some void behind the barrel end face as you say to avoid eddies, this was in a shrouded barrel so protecting the crown was not so important - if I am honest it made no difference to that particular barrel.

For those that believe in the theory of air strippers would they not work better if the barrel end was shaped like the cone of the stripper so the two cones met at their points with just less than a pellets length gap thus allowing maxium free space to allow the turbulent air out?