Exactly, connecting the two shock towers, so the fix doesn't rely on the weak sheet metal underneath.Here is what I copied from another E46F member, I believe it's the best method.
Notice how the main rectangle tube is cut through and goes down about one inch into the trunk floor. This gets welded to both the bottom & top sheet metal, making for a very rigid platform. Then of course all the other structural material is weld in to tie everything into the shock towers. Take a close look at all the pics, you'll see what I mean.
Pulling down on acceleration.If i'm remembering correctly, the engine rotates clockwise, making torque under wheel resistance push UP on the driver's side floor pan. Clearly the metal will see force in both directions, but the majority of the force it sees will be pushing your plate up, not pulling it down.