My 20 bore has a 31" bl., 1.1" breech and .825" muzzle, so very similar taper to yours.
I have no rear sight and my front sight is .115" tall and it's about on at 25 and 50 yards.
My aim is the front sight above the 'rear of the breech' & the ball hitting on the top of the 'blade'.
It is best to start with a slightly higher front sight and file it down as needed.
I would suggest .200" high would be a good 'starting place', but .250" would be safer.