I confirm, if this rempart is mostly horizontal, the horizon will be where the lines cross, way up above the picture.
To view a girl laying on a merlon like this, from above, the viewer has to be higher so you can't draw it as if it was viewed a human height.
Whatever you draw in the top left corner, it has to be seen from a point of view 3 meter above the girl.
I'd almost go three-point perspective on this, using a huge canvas during work since the vanishing points are very far off the picture.