Tilt the saddle nose up little by little until the rider quits sliding forward.

If the saddle is tilted too far back (visually) for your liking, try a different brand/model of saddle.

There are really three cases...

Nose to far down, riders slides forward.

Saddle is level, rider doesn't slide either way.

Nose too far up, rider slides backwards.

But level does NOT mean visually level. Level is when you don't slide. Since most saddle dip in the middle, the part where your weight rests has to be the part that is level.