These are more properly called perimeter drains. There are two versions of a French drain, one named after Mr. French, and the other apparently refers to a type of drain used in France. Or so I am told. In any case, it is very common to lay the tile flat in a perimeter drain. The water will move from higher elevation to lower elevation, which is presumably a sump pit, or there is a drain which connects to the street in one corner, which collects all the groundwater from the four sides of the house.