Well it turned out to be easier than I thought. "After" pic attached.
What I did was to shorten both screws in the rear corners to pull them out of the "shut" equation. Then I shortened the main catch to the point where it no longer latches and then went a tad longer until I got a strong latching and clean releasing action (involves some centering of the main latch).
At this point nothing had changed. So I moved to the right-side hinge.
When you loosen the two bolts on this hinge, the engine cover will want to slide toward the clam. It won't make contact but to avoid stressing the other hinge connection and just to be safe you should fold and stuff a wash sponge between the cover and clam so the sponge is fully supporting the clam when it comes loose. Also, in my case, "centered" on this hinge meant "all the way rear", so it was easy for me to keep track of the original position. YMMV
I loosened, but didn't remove, the two bolts then slid the shim into place, keeping everything straight and even as I tighten the two bolts back down. I ended up needing two shims (P/N A122B0199F). It is now symmetrical, which is what I was after. "Flush" may not be possible, or I think one might need longer screws for the hinge... and maybe I'll tackle that one day but right now I am totally happy with "even", "level" and "symmetrical".
Then I went back and lengthened the rear corner screws (the ones with the rubber cap) until tapping on each corner when shut not longer caused any kind of rattle.
Only thing I wish now is to get a more "shut" engine cover. The rear of the cover feels like it sits a tad bit high. But I if I compress the spring any more than it is then for some reason it does not latch. I guess it's not a huge deal but I know I've seen cleaner shut lines on these engine covers on other cars.
Last edited by Smoky; 04-11-2019 at 11:44 AM.