I like "bevel up", but if I thought "bevel down" worked better that's what I would do. Or in other words, try both.
Also, positioning the flint forward or back in the jaws needs to be experimented with. Don't assume "way back" is the correct position. Getting the flint close to the pan works for me, but that will depend on the length of the flint. But all locks are different, some need more of a "run" at the frizzen.
My Bess sparks better with the flint as far forward as possible. My Jeager doesn't seem to care where it is.