There is no way to make them fit perfectly, because they curve out more in the middle...in fact they are overall thicker then the stock red rear lense covers.
I found a partial cure by sanding off the prongs or tabs on the back of the new clear lenses, and sanding down (with a grinder) about 1/2 the thickness of the entire plastic backing on the new clear lenses. Do it carefully, I cut through on of my first ordered clear lenses (second order $35) but well worth it, because I, like you, was not happy with the fit. Its not perfect now, but much better, and I do love the look of clear lenses on my black VX...all but my taillights are clear.
Rob A.