It seems like the current Software Update nullified my tweak (YMMV). I think this might be helpful as most of the results showed only how to “disable sleep when the lid is closed” vs. disabling wake on lid open.
Anyways, to do so, do the following in your Terminal (Application > Utilities > Terminal.app):
Check current state (i.e. “lidwake”):
$ pmset -g
$ sudo pmset -a lidwake 0
Or put it back to normal (re-enable):
$ sudo pmset -a lidwake 1
Check the current state again to verify (i.e. “pmset ‑g”). You shouldn’t have to restart. I hope that helps. Would’ve saved me a couple of minutes for sure.