I think this may be the easiest way to get that pesky plug out. If you look at the profile of the plug, you'll see that it's not even half the height of any other nut or bolt head in that size. Now look at the socket you're using--it has shoulders sloping inward all around, which means any grip you're getting on the sides of that hexagon is just in your imagination.
I took a 15/16 six-sided socket to my bench grinder and in no time was rid of the shoulders. Took that plug right out.
I took a 15/16 six-sided socket to my bench grinder and in no time was rid of the shoulders. Took that plug right out.