Does the flint on a flintlockneed a razor edge to function properly?

I cleaned the flint and frizzen with analcohol patch the night before
shooting the rifle. When I got to the range it shot twice, and then it
wouldn't ignite the prime. Luckily the flint was a double edge flint, so
I turned it around and shot the rest of the day. The edge still looked
pretty good compared to the other end of the flint.Do I needto knapp
theside that wouldn't shoot?

When mounting the flint in the cock, should the flint be against the
frizzen at half cock, or backed off the frizzen a bit? When I got the
the rifle it had a gap about the thickness of a paper match stem
between the flint & frizzen at half cockis the reason I ask.

Thanks.