Couple of things that would make life simpler:
1. Remove the engine bay strut brace on that side of the engine. Takes less than a minute and means you can get a socket squarely onto that rear nut without the chance of rounding it off.
2. The smaller plastic engine cover sits over the top of the one you removed and the edges interlock. For the sake of another minute, remove that too, so you are not having to twist the main cover out from underneath it.