How should feet be positioned on the pedals?

That perspective is over-simplified. Like ever choice there are pros and cons.

On-the-ball riding affords the potential to rapidly change the force by moving the ankle joint. Without this, the inertia of the leg limits the rate of change.

Sudden drops in the terrain can be accommodated by extending the ankle joint in situations where the instep rider’s foot would come off the pedal.

The Achilles tendon can also efficiently recover much more of the energy in such situations when riding on the ball of the foot.

I’ve been working on increasing my speed prior to forward jumps. I found that riding closer to the toes helps me to pedal faster.