In this type french drain, about a foot of concrete around the inside perimeter of the basement was dug up, the french drain (and probably gravel around it) installed and another layer of concrete installed on top. Some have sump pumps connected to the system but this one doesn't doesn't prob because of the slope.
It is not exactly this system, but it looks similar in that there is a piece between the floor and the wall and there is a layer of concrete covering it.
The patch layer of concrete over the drains isn't level with the main part of the basement and I've no idea how thick it is. It was done 2 owners ago.
The contractors around here don't seem very familiar with it.