I don't know how to vent with a axial view unfortunately. I normally look at the outline from the side.
Festae are pretty easy to sex without venting. You'll get better answers if you provide a side view of the fish.
Here is a male, steep profile, no dark area in the dorsal
Below a couple females
Note in both females the more torpedo shape, and dark color in the anterior of the dorsal fin.
another shot below of a female, without a male in the tank
as soon as the male is returned to the tank, her colors brighten up