Weird. My browser did not show Nemo's response until the forum told me to reload.
I am all you got? I have a bad feeling about this!
Your images look good to me. Did they not quite fit perfectly, so you made two? Virtually all factory spoilers are only for looks. My HX came with one and so did my dad's Focus SFE. Mine also has lean burn and light alloy wheels. His has an active grill block and smooth wheel covers. I know that one Civic owner swapped trunk lids with someone without the spoiler, but if you simply remove it, you have open bolt holes, which would work great to mount a Kamm-back.
Having the block in front of the grill should be more aerodynamic than behind, although I do not know how much of a difference it would make. I would think that it would be different with wheel covers, since they would spiral in constantly-varying relation to the wind. I imagine that most of the problem is with air swirling around the outer edge of the wheel, not crossing from one side to another.
A partial bellypan should provide part of the benefit of a full one.