Is it better to build your french drain at the at the base of the mound (an elevated leaching field) where the water comes down and toward the house or nearer the foundation you are trying to protect?
It’s better to install your French drain at the point you are trying to drain.
If you are protecting a basement, I’d install the drainpipe BELOW the concrete basement slab a minimum of 5-6”.
Remember, water will go in the direction of least resistance. When it’s moving through the soil/rock and hits the drainpipe, it will flow in the pipe much faster than in the soil/rock, thus causing the water to flow towards the pipe.
Water can move sideways through the soil or it can rise up through the soil from a rising watertable.