1)It is not all about vortex formation. To be more precise, sometimes you try to exploit vortices that are already generated because of the wings or because of the bargeboards.
Typical example are the semiciricular channels at the footplate of the front wing endplates: they are ther to house and guide a vortex the tip vortex of the wing.
2) not all the vortices form the front wing make theiru way to the floor. The t-tray produces vortices, the brageborad produces vortices, and those are fed under the floor.
The ttray is a rectangular shaped almost flat plate with higher pressure on top and low on the bottom: tip vortices develop on its two side and go under the floor running along the side of the inner step of the floor
The bargebord has to be seen like a delta wing rotated 90° that relases two vortices, one of which goes under the floor.
The sucion peak at the leading edge of the floor is due to acceleration of the flow around the round edge, like in an airfoil.
When bargebard and ttray vortices flow in this already low pressure region, thy get squeezed and their downforce contribution is enhanced.
Seeing this effect, one could get tempted of squeezing these vortices more... and so ends up putting exhausts there maybe.